Playlists

[toroidal-code]

We're going to need some way of queuing music for playing, and possibly saving these queues.

This would involve:

• Writing a Playlists model (id, name, has_many tracks, etc.)
• Writing the model validations and validation specs
• Guaranteeing the existence of the Queue playlist and always being at id = 1
• Creating add methods Playlist
• Creating shuffle method for Album, Artist, and Playlist that will add them to the queue out of order, but not modify the existing order of the queue.
• Creating basic CRUD API methods for Playlists, with a special path for the queue
• A PlaylistTrack model to keep order
• Add the queue_tracks.
• Add validations that only the Queue (id=1) can have queue_tracks.