Add album artist

Use a track's album-artist tag as the artist for the album.

If the album-artist isn't present, fallback to the track artist for the album.  
Also, the UI now searches based on the album and track artist id, instead of the artist.
This means tracks whose artists who appear on albums for which they are not the album-artist will now show up in the artists track listing.

Also removed AAC tag classes as jaudiotagger supports m4a (mp4, aac, etc..) tags.