fix layout

#### Rough

- [x] header
- [x] footer
- [x] support gratipay notice
- [x] content pages like about pages
- [x] two-column things like charts and FAQ
- [x] profiles
- [x] community pages
- [x] all communities listing `/for/`

#### Finish

- [ ] penny background
- [ ] min height (no empty space below footer)
- [ ] signing out fails?
- [ ] clean up logo + stats in header
- [ ] figure out column story
- [ ] responsiveness
- [ ] refactor SCSS
- [ ] harmonize markup/scss between homepage and inside pages