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

Demo

• Test live at http://funkwhale.pages.funkwhale.audio/-/funkwhale/-/jobs/38563/artifacts/front-review/index.html

Peek_2019-12-22_16-56