[WIP] New playlist functionality

:construction: Work in progress!

Ready:

- [x] Sidebar with playlists
- [x] Hardcoded playlists
- [x] Hardcoded song display
- [x] Playlist - Database connection
- [x] Create basic playlist functionalities (create, edit, delete playlist)

Working on:

- [ ] Play the next song in the playlist after the current song

To do:

- [ ] Unit tests

Playlists will:

- [ ] Repeat playlist songs

Playlists may:

- [ ] be sorted by dragging

... and will be updated
Maybe the issue is related to the three instances of a controller. I never had such a setup.