* Harmonize footers across devhub (and frontend pages a bit more)
Changes:
- Copy over fonts from addons-frontend, use Inter everywhere
- Use photon-footer everywhere, adding a light blue margin before
to make the transition less aggressive and match header
- Fix error pages block to align content correctly
- Translate strings in footer
* Add basic infrastructure, configure fonts
* First version of navigation and section header.
Fixes#3849 (Navigation)
Fixes#3850 (Customize Firefox Section)