Implemented context menus in GridView items in AlbumListFragment,
ArtistListFragment and AudioGenreListFragment.
This allows the user to add everything from an artist, album, or
genre by popping up the context menu and selecting either play
or Add to playlist.
Created a new class utils/MediaManager to hold any methods related
to managing media. Added methods play(...) and queueAudio(...) to
add musiclist items to the current playlist and start playing.
a7874de0e4