macosx: Publicly define protocols of VLCLibraryAudioDataSource
requested to merge claucambra/vlc:work/publically-define-protocol-vlclibraryaudioatasource into master
Not having the table view and collection view data source/delegate protocols defined publicly in the header can cause unnecessary warnings when trying to assign VLCLibraryAudioDataSource as the delegate or data source for other objects
Signed-off-by: Claudio Cambra developer@claudiocambra.com