Improves header even-ness at mid-sizes
Restore bottom margin to nav at mid sizes
Merge branch 'ko-midHeader' of https://github.com/kennethormandy/crosswalk-website-v2 into kennethormandy-ko-midHeader
 Improved home page for small screens

 - Drop red getting-started box
 - Improved layout of blue get-started button
Merge branch 'kennethormandy-ko-midHeader'