Enable middleman-autoprefixer to create vendor prefixes

* Add `middleman-autoprefixer` to `Gemfile`
* Configure `middleman-autoprefixer` in `config.rb`
* Disable `bourbon` prefixes in base settings

https://trello.com/c/Ex4aRfuZ
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
- Consolidate stylesheets
Add markup and copy for open-source community section

* Add basic style layout for the community section
* Add community icons
* Change layout of the community section
* Add button to section and clean up responsive style
* Uncomment social links in landing page
Move stylesheets to modules folder
Add global nav partial to index and featured social media links
remove community icons and restructure community section
Add width to subtitle, call in locales, and reduce font size
Reduce footer p size