[GSoC 2019]Medialibrary Stub: logic implementation

Description

This MR completes the previous introduction of an empty medialibrary stub. It adds the logic to mimic the medialibrary behaviour.

The first commit removes the hard coded fake samples, and now allows the medialibrary stub to load fake samples from a json file. It also adds a script to generate said json file.

The second commit implements the medialibrary logic into the stub.

To start a session with the stub active, vlc must be started with the intent extra extra_test_stubs set to true. This can be done from the command line with:

'adb shell am start -n org.videolan.vlc.debug/org.videolan.vlc.StartActivity "--ez ''extra_test_stubs'' true"'

How Has This Been Tested?

This has been tested by loading a few albums from differents artists to the phone, creating a json file with the same medias, and then comparing the logic between both for the sample samples view by view.