FLE site now mobile-friendly

* Converted over to bootstrap 3 completely
* deleted some (not all) unused styling and unnecessary HTML
* deleted unused images (also converted nav bar to put html and css vs using images

key changes:

* nav bar is now collapsible vs simply hiding it's own options on mobile
* footer no longer collapses on itself
* using media queries to look good on desktop, tablet, and mobile

persisting issues:

* footer still is not sticky and has a large bottom margin that I can't get rid of (gahhhhH!!!!!!!!!) 
* have not yet written new style guide in the GitHub wiki even though I edited the README to say to look there. I'll do that soonish.