Set audio player elevation

vlc-android/res/layout/info_activity.xml

@@ -163,6 +163,7 @@
             android:id="@+id/audio_player_container"
             android:layout_width="match_parent"
             android:layout_height="match_parent"
+            android:elevation="@dimen/audio_player_elevation"
             android:visibility="gone"
             vlc:layout_behavior="android.support.design.widget.BottomSheetBehavior">
             <android.support.v7.widget.ViewStubCompat

vlc-android/res/layout/playlist_activity.xml

@@ -80,6 +80,7 @@
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:visibility="gone"
+            android:elevation="@dimen/audio_player_elevation"
             vlc:layout_behavior="android.support.design.widget.BottomSheetBehavior">
             <android.support.v7.widget.ViewStubCompat
                 android:id="@+id/audio_player_stub"

vlc-android/res/values/dimens.xml

@@ -70,4 +70,5 @@
     <dimen name="fastscroller_track_width">6dp</dimen>
     <dimen name="fastscroller_track_padding">5dp</dimen>
     <dimen name="audio_player_cover_margin">30dp</dimen>
+    <dimen name="audio_player_elevation">16dp</dimen>
 </resources>
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