HTML5: use less instead of plain css

Using connect-assets to automatically compile less files into css files and
serve them. All less files should be under assets/css/.
The current layout file is using less but it's a plain css, with its content
simply copied from the old layout.css file.
HTML5: setup bootstrap and update font-awesome

Versions:
- Bootstrap v3.0.1
- Font Awesome 4.0.1

Haven't added bootstrap-theme, can be add in the future if needed.
Merge pull request #289 from daronco/html5-bridge-layout-setup

HTML5 layout with bootstrap