Feature: (Non-) Strict Playlists

[perzeuss]

We have defined two sorts of mBat Playlists:

1. strict: Playlists contain only tracks everyone in the group has in their spotify library. Everyone can remove tracks from this palylist by removing them from their library.
2. non strict: Playlists contain tracks anyone in the group has in their spotify library. They are sorted descencing depending on how many users have the tracks in their spotify library. This helps getting more tracks into the playlists.

Feel free to discuss your ideas or thoughts about this feature here with others!