Add Sass and Cleanup Styling

Lots of things happened here, which hopefully you can see through the commits, but here is a breakdown:

1.  Moved all third-party CSS to /css/vendors/
2.  Split custom styling from prototype into Sass files. main.scss collects all partials and base styling (colors, fonts, etc). and gets compiled into main.css, which is what actually gets used.
3.  Went through and restructured some UI and layout items, including the footer (so it'll display persistently at the bottom of the page or below content), header areas, and replaced custom code with Bootstrap's existing helpers or styling, where possible.
4.  Added in modules to control defining lots of big things, like buttons and links.
5.  Start styling stuff so it looks like the design treatments.