- Handle all plausible cases of assigning into the playlist
- Allow changing the current track to an existing one on the playlist
- Allow getting playlist as a real array instead of an array-like proxy
(Could be useful for storing it to a WML variable, for example)
- Allow removing a track by index and fixup the "set track" interface
- Commit music changes only after event completes, not after any control=flow tag is executed
- Allow inserting a track into the middle of the playlist
- Allow assigning a config to an existing track to overwrite it
- Use std::find when checking for duplicate tracks
