Update font awesome files

Staged at:
http://awesome.dart-lang.appspot.com/

The headings on the homepage look different, but maybe that's related to the font change you made recently. Scary. Also, the update broke the "Get Dart tools" button on the homepage (making it two rows), so I shortened its text and, while I was there, changed the icon.

I updated so I could get access to new icons such as icon-desktop and icon-mobile-phone. Plus up-to-date is good, right? For more info on what changed, see http://fortawesome.github.io/Font-Awesome/#whats-new.

Review URL: https://chromiumcodereview.appspot.com/14713008