Bump bootstrap to 3.3.1

* update gemspec to use twitter bootstrap sass gem (and sass-rails)
* revamp layout to use bootstrap 3.3 conventions to get a collapsable mobile (small browser) nav
* update local overrides to match the new layout
* updated README with notes about the new bootstrap includes
* remove glyphicon font files because they are in the bootstrap-sass gem
* add bootstrap include to engine so consuming apps can use it