LibraryAlbum: move code from dealloc->didTurnIntoFault
- Recommended by Apple for CoreData NSManagedObjects
LibraryViewAlbumCell: do alt-text and cover updating in an KVO observer
- This is more consistent with what we do with Track/Artist cells
- Also fixes a third of bug #37 (the track counts for albums)
  - the KVO observer fires when a track gets added or deleted
    so the track counts are recalculated