Stop using [playlist -items]

Change-Id: Ie5a603070febee7ca0dda434aa633b30215a365a
Implement SPTrack -hash and -isEqual:.

Change-Id: I8c7ef4995a562ba968982dbe7a6e12af5ca9c45b
Make [SPPlaylistContainer -flattenedPlaylists] KVO'able

Change-Id: Ifa6a959822a94045f30b4871c3d77a1b489dc2d6