header.php: add markup for mobile menu
Mobile navigation:
	- jquery dependency
	- uses input elements in header.php
Refactor mobile nav:
	- remove input elements in header.php - replace with div
	- javascript less specific
	- hide menu on desktop
	- remove margin on ul
bug: iOS safari flashes black on some clicks but works fine
*a note on JS*
JS dependency is not ideal as mobile nav will break without it also mobile-menu icon color is set in js via addcss();