Playlist tracks in data model isn't correct

[NattyNarwhal]

Tracks are an unordered set in a playlist, which is not quite right. playlistIndex is used as a crutch to deal with that. An ordered set would work, except it precludes duplicate entries of the same track. The corresponding inverse relation isn't quite right iehter, as it's track to single playlist.

See if changing the relations would work. It may involve storing tracks as [Something] transformables.