Update marketing pages and colors/style

This marketing page more closely matches the designs
from @dutchashell.  Update the colors and fonts, and
also update the headers to to match the designs.

Still waiting on images and icons, but this is the basic
framework.
Merge branch 'devel' into feature/marketing-page

Update nav-4 and header color/size
Fix rspec tests and merge conflicts

Tests now run again
Merge pull request #266 from 18F/feature/marketing-page

Update marketing pages and colors/style