feat: Add global sidebar

[dcramer]

This moves us towards the ability to start defining views at the global level rather than per repository.

[dcramer]

A few problems right now:

1. sidebar needs fixed/scrollable
2. logout/settings icons ideally go at bottom of sidebar
3. footer needs pushed at least all the way to the bottom (ideally); on short pages it ends up pulled up

[dcramer]

I'm not fully convinced this is a good idea since some pages will actually really weird if you didn't render them repo specific. It's possible we dont need all of those pages, but some like repository coverage are extremely useful. I dont know how we'd make those as functional without selecting a repo, and then if we have to force selection it ends up a bit wonky too.

[dcramer]