43616727: Stub out home#index in application layout with a login/register link
43617127 & 43617163: Login/signup page, redirected to a stubbed dashboard#index page

* Nav helper for highlighting current page
* Added simple_form config so it works with Bootstrap
* Added dashboard placeholder
* Separate public and admin styles: all of Twitter Bootstrap for admin styling, public-facing forms & alerts use some Bootstrap modules
* Susy for grids