[WIP] New playlist functionality

:construction: Work in progress!

Ready:

- [x] Sidebar with playlists
- [x] Hardcoded playlists
- [x] Hardcoded song display

Working on:

- [ ] Playlist - Database connection
- [ ] Create basic playlist functionalities (create, edit, delete playlist)

To do:

- [ ] Play the next song in the playlist after the current song


Playlists will:

- [ ] Repeat playlist songs

Playlists may:

- [ ] be sorted by dragging

... and will be updated
@MorrisJobke Could you have a look at the issue above?

Also are you available today on IRC to talk about "add to playlist" controls next to songs?