Add nav partial and move nav markup to partial

- Rename navigation partials to be more semantic
- Change href links to use link_to method
- Add contribute translation
- Rename classes in nav
- Change hover color of cta in nav
- Change contribute pathway
- Move logo link to one line
- Move logo link to two lines
- Update nav to docs
- Move code style from layout to typography
- Add new side-nav stylesheet and align doc elements
- Update header typography styles in docs
- Add search bar to docs