Playlist now fully support episodes

[felix-hilden]

Playlists support episodes in all calls. So we should definitely do something about that.

Names like playlist_tracks_... are a bit odd now. They could be changed to items or simply playlist_... if they are clear enough. We should also think about having only generic methods that accept URIs vs. specialised that accept IDs, or have both. But having only specialised would be odd, because filling a playlist with multiple types would require more calls.

[felix-hilden]

The calls that are affected with their relevant parameters are:

• playlist_tracks
• playlist_tracks_add(track_ids)
• playlist_tracks_clear
• playlist_tracks_remove(track_ids)
• playlist_tracks_remove_indices
• playlist_tracks_remove_occurrences(track_refs)
• playlist_tracks_reorder
• playlist_tracks_replace(track_ids)

I think the best thing to do is to shorten the names and change ID arguments to URIs. It shouldn't be too big of a burden on users, because the URIs are already provided in track objects, and conversion from other sources is easy. But the names would be a lot cleaner.

• playlist_items
• playlist_add(uris)
• playlist_clear
• playlist_remove(uris)
• playlist_remove_indices
• playlist_remove_occurrences(refs) (refs with uris)
• playlist_reorder
• playlist_replace(uris)

One thing we could do is simply deprecate the existing functions, because they are not invalid, and let them use the new ones internally.