macosx: Bring video and audio library improvements to media source library
This MR contains a set of improvements and refactors for the media source library views that bring it in-line with the video and audio libraries. Mainly:
- Setup and view switching code has been moved into a dedicated VLCLibraryMediaSourceViewController class
- The media source components now live in the "library" folder, along with the "audio-library" and "video-library" components
- The collection view for the media source now has dynamic item sizing like the audio and video library collection views
Signed-off-by: Claudio Cambra developer@claudiocambra.com