Add header misc. stuff
WIP: Header Nav
Mobile menu functionality and style fixes
Some tidying of the main nav code
Merge from upstream

- Adjusts Grunt tasks to prevent autoprefixer choking on merge
  conflict characters. Needs further research.

Conflicts:
	static/css/main.css
	static/css/main.ie.css
	static/css/main.ie.min.css
	static/css/main.min.css
Update menu icon to use cf-icons
Tweaks from code review
Simplify header/logo margins
Merge pull request #151 from Scotchester/header-nav

Primary navigation
Fixes merge conflict.