[wip] Pile of design tweaks and fixes

There was a triage recently, but I'm not sure anything got written down. I'm keeping this open for the quick-fixes folks were asking for. 

So far I remember we wanted to:

- [x] make "Sign in" blue on hover on login page
- [x] move main nav left
- [x] make active nav link blue
- [ ] update favicon

@iamjessklein what else was there?