Changes to sticky navs

Buncha changes:
- header sticky nav now uses existing "navbar-categories" and "global-nav" menu locations, instead of instantiating a new "sticky-nav" location*
- header sticky nav has been restyled to look more like the wireframe
- footer nav is now dismissable

Still to do:
- revamp stickynav for phones to use a menu in the upper left, rather than the current approach (which messily mirrors the main navbar and is problematic)
- clean up "follow" URLs and icons in lower right

Let me know if this is moving in the right direction...