Resolve "Redesign the sidebar/navigation to simplify the UI"
Closes #594 (closed)
Cf https://governance.funkwhale.audio/d/m9LlGf4T/redesign-of-the-sidebar-navigation:
- Revamped navigation (no more fixed bar when browsing library)
- Split between personal/public stuff
- Narrower sidebar
- Dedicated player/queue mode (also cf #703 (closed))
- Bottom attached player