Update to Font Awesome 3 and rename the font-awesome-ie7.less

This pull request updates the twitter-bootstrap-rails gem to use Font Awesome 3 and rename the font-awesome-ie7.less to fontawesome-ie7.less to match the fontawesome.less file naming format


Please note that on a Ruby/Rails programming scale of 1-10 I'm a 3 and, besides a few small changes contributed in the past to this gems erb templates, I'm new to modifying and contributing to gems.  My point is please make sure to test this before merging it. While I've tested it on my system multiple times and it works I'm still so green at this I might be missing something obvious. I would also appreciate any feedback, thanks!