macosx: Unify collection view item types

This PR helps significantly eliminate duplicate code and reduce coupling between specific media item types and the views that operate on them

This is possible thanks to the use of a new VLCMediaLibraryItemProtocol

modules/gui/macosx/UI/VLCLibraryCollectionViewAlbumItem.xib

-<?xml version="1.0" encoding="UTF-8"?>
-<document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="14490.70" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none" useAutolayout="YES" customObjectInstantitationMethod="direct">
-    <dependencies>
-        <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="14490.70"/>
-        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
-    </dependencies>
-    <objects>
-        <customObject id="-2" userLabel="File's Owner" customClass="VLCLibraryCollectionViewAlbumItem">
-            <connections>
-                <outlet property="addToPlaylistButton" destination="Ubz-8I-W2F" id="k0q-b1-PZi"/>
-                <outlet property="annotationTextField" destination="tm2-NW-WsZ" id="Miy-RS-Rol"/>
-                <outlet property="durationTextField" destination="VAn-gF-QiZ" id="U8T-Cs-HaL"/>
-                <outlet property="mediaImageView" destination="2aB-sB-hfY" id="Sv0-G1-KNm"/>
-                <outlet property="mediaTitleTextField" destination="OBS-Eh-1mT" id="h1n-PU-IAx"/>
-                <outlet property="playInstantlyButton" destination="S3I-5Z-qgS" id="JlC-bE-i5Y"/>
-                <outlet property="progressIndicator" destination="dFt-oZ-h9P" id="JC6-gk-Mid"/>
-                <outlet property="unplayedIndicatorTextField" destination="u2r-zy-XEW" id="56s-K4-Kxr"/>
-                <outlet property="view" destination="Hz6-mo-xeY" id="0bl-1N-x8E"/>
-            </connections>
-        </customObject>
-        <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
-        <customObject id="-3" userLabel="Application" customClass="NSObject"/>
-        <customView id="Hz6-mo-xeY" customClass="VLCTrackingView">
-            <rect key="frame" x="0.0" y="0.0" width="256" height="214"/>
-            <autoresizingMask key="autoresizingMask" flexibleMaxX="YES" flexibleMinY="YES"/>
-            <subviews>
-                <customView translatesAutoresizingMaskIntoConstraints="NO" id="2aB-sB-hfY" customClass="VLCImageView">
-                    <rect key="frame" x="0.0" y="49" width="256" height="165"/>
-                    <subviews>
-                        <customView translatesAutoresizingMaskIntoConstraints="NO" id="dFt-oZ-h9P" customClass="VLCLinearProgressIndicator">
-                            <rect key="frame" x="0.0" y="0.0" width="256" height="4"/>
-                            <constraints>
-                                <constraint firstAttribute="height" constant="4" id="lyQ-kl-gVk"/>
-                            </constraints>
-                        </customView>
-                        <button verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="S3I-5Z-qgS">
-                            <rect key="frame" x="96" y="51" width="64" height="64"/>
-                            <buttonCell key="cell" type="square" bezelStyle="shadowlessSquare" image="libraryPlay" imagePosition="only" alignment="center" inset="2" id="IHP-p1-d0R">
-                                <behavior key="behavior" pushIn="YES" lightByBackground="YES" lightByGray="YES"/>
-                                <font key="font" metaFont="system"/>
-                            </buttonCell>
-                            <connections>
-                                <action selector="playInstantly:" target="-2" id="E2B-oj-rx3"/>
-                            </connections>
-                        </button>
-                        <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="tm2-NW-WsZ" customClass="VLCRoundedCornerTextField">
-                            <rect key="frame" x="8" y="141" width="37" height="17"/>
-                            <textFieldCell key="cell" lineBreakMode="clipping" title="Label" id="tyb-Ur-7J9">
-                                <font key="font" metaFont="system"/>
-                                <color key="textColor" name="labelColor" catalog="System" colorSpace="catalog"/>
-                                <color key="backgroundColor" name="textBackgroundColor" catalog="System" colorSpace="catalog"/>
-                            </textFieldCell>
-                        </textField>
-                    </subviews>
-                    <constraints>
-                        <constraint firstAttribute="bottom" secondItem="dFt-oZ-h9P" secondAttribute="bottom" id="4q3-3S-7PA"/>
-                        <constraint firstItem="S3I-5Z-qgS" firstAttribute="centerX" secondItem="2aB-sB-hfY" secondAttribute="centerX" id="Seo-tS-piW"/>
-                        <constraint firstItem="S3I-5Z-qgS" firstAttribute="centerY" secondItem="2aB-sB-hfY" secondAttribute="centerY" id="ZWU-oW-OVa"/>
-                        <constraint firstItem="dFt-oZ-h9P" firstAttribute="leading" secondItem="2aB-sB-hfY" secondAttribute="leading" id="gTe-sx-hdP"/>
-                        <constraint firstAttribute="trailing" secondItem="dFt-oZ-h9P" secondAttribute="trailing" id="kBI-UU-vnc"/>
-                    </constraints>
-                </customView>
-                <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="OBS-Eh-1mT">
-                    <rect key="frame" x="-2" y="21" width="52" height="24"/>
-                    <textFieldCell key="cell" scrollable="YES" lineBreakMode="clipping" title="Label" usesSingleLineMode="YES" id="7Hy-o3-LvX">
-                        <font key="font" size="20" name=".AppleSystemUIFont"/>
-                        <color key="textColor" name="labelColor" catalog="System" colorSpace="catalog"/>
-                        <color key="backgroundColor" name="textBackgroundColor" catalog="System" colorSpace="catalog"/>
-                    </textFieldCell>
-                </textField>
-                <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="u2r-zy-XEW">
-                    <rect key="frame" x="224" y="1" width="34" height="17"/>
-                    <textFieldCell key="cell" lineBreakMode="clipping" title="NEW" id="NeT-5U-eZn">
-                        <font key="font" metaFont="system"/>
-                        <color key="textColor" name="labelColor" catalog="System" colorSpace="catalog"/>
-                        <color key="backgroundColor" name="textBackgroundColor" catalog="System" colorSpace="catalog"/>
-                    </textFieldCell>
-                </textField>
-                <button verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="Ubz-8I-W2F">
-                    <rect key="frame" x="222" y="187" width="20" height="20"/>
-                    <constraints>
-                        <constraint firstAttribute="width" constant="20" id="XhX-7U-Nxj"/>
-                        <constraint firstAttribute="height" constant="20" id="ZDT-YM-Cbr"/>
-                    </constraints>
-                    <buttonCell key="cell" type="square" bezelStyle="shadowlessSquare" image="ellipsis" imagePosition="only" alignment="center" inset="2" id="6ko-MM-ds0">
-                        <behavior key="behavior" pushIn="YES" lightByBackground="YES" lightByGray="YES"/>
-                        <font key="font" metaFont="system"/>
-                    </buttonCell>
-                    <connections>
-                        <action selector="addToPlaylist:" target="-2" id="2C9-Rn-VAb"/>
-                    </connections>
-                </button>
-                <textField horizontalHuggingPriority="251" verticalHuggingPriority="750" translatesAutoresizingMaskIntoConstraints="NO" id="VAn-gF-QiZ">
-                    <rect key="frame" x="-2" y="0.0" width="42" height="19"/>
-                    <textFieldCell key="cell" lineBreakMode="clipping" title="Label" id="LSS-jh-llZ">
-                        <font key="font" size="15" name=".AppleSystemUIFont"/>
-                        <color key="textColor" name="labelColor" catalog="System" colorSpace="catalog"/>
-                        <color key="backgroundColor" name="textBackgroundColor" catalog="System" colorSpace="catalog"/>
-                    </textFieldCell>
-                </textField>
-            </subviews>
-            <constraints>
-                <constraint firstItem="2aB-sB-hfY" firstAttribute="top" secondItem="Hz6-mo-xeY" secondAttribute="top" id="3Ah-0T-rA9"/>
-                <constraint firstAttribute="trailing" relation="greaterThanOrEqual" secondItem="OBS-Eh-1mT" secondAttribute="trailing" id="457-oy-EbD"/>
-                <constraint firstItem="Ubz-8I-W2F" firstAttribute="top" secondItem="Hz6-mo-xeY" secondAttribute="top" constant="7" id="8Qf-Un-Gdl"/>
-                <constraint firstItem="VAn-gF-QiZ" firstAttribute="top" secondItem="OBS-Eh-1mT" secondAttribute="bottom" constant="2" id="ALi-0z-Mza"/>
-                <constraint firstAttribute="trailing" secondItem="u2r-zy-XEW" secondAttribute="trailing" id="Dd7-va-0UJ"/>
-                <constraint firstItem="u2r-zy-XEW" firstAttribute="centerY" secondItem="VAn-gF-QiZ" secondAttribute="centerY" id="H5N-j9-THf"/>
-                <constraint firstAttribute="bottom" secondItem="VAn-gF-QiZ" secondAttribute="bottom" id="Kp0-Hx-3Ek"/>
-                <constraint firstItem="VAn-gF-QiZ" firstAttribute="leading" secondItem="Hz6-mo-xeY" secondAttribute="leading" id="QUW-dn-Fbc"/>
-                <constraint firstAttribute="trailing" secondItem="Ubz-8I-W2F" secondAttribute="trailing" constant="14" id="ZVz-SL-rxZ"/>
-                <constraint firstItem="tm2-NW-WsZ" firstAttribute="top" secondItem="Hz6-mo-xeY" secondAttribute="top" constant="7" id="cvk-A5-enS"/>
-                <constraint firstItem="tm2-NW-WsZ" firstAttribute="leading" secondItem="Hz6-mo-xeY" secondAttribute="leading" constant="10" id="fH0-Om-7gV"/>
-                <constraint firstAttribute="trailing" secondItem="2aB-sB-hfY" secondAttribute="trailing" id="oZw-Ab-83p"/>
-                <constraint firstItem="2aB-sB-hfY" firstAttribute="leading" secondItem="Hz6-mo-xeY" secondAttribute="leading" id="t9g-tX-AQX"/>
-                <constraint firstItem="OBS-Eh-1mT" firstAttribute="top" secondItem="2aB-sB-hfY" secondAttribute="bottom" constant="4" id="vJy-Kf-4Jh"/>
-                <constraint firstItem="OBS-Eh-1mT" firstAttribute="leading" secondItem="Hz6-mo-xeY" secondAttribute="leading" id="yvp-xr-geN"/>
-            </constraints>
-        </customView>
-    </objects>
-    <resources>
-        <image name="ellipsis" width="17" height="3"/>
-        <image name="libraryPlay" width="64" height="64"/>
-    </resources>
-</document>