[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
- [ ] Add songs by drag&drop

Playlists will:

- [ ] Repeat playlist songs

Playlists may:

- [ ] be sorted by dragging

... and will be updated
This is needed because the entity needs to be filled by querying another table, group the result and inject it into the object. Should be done by the businesslayer later.