Assets setup

Add React JS and Foundation. Also specified a Ruby version (for people using rbenv at least, not sure how it exactly works with rvm). Also removed the Coffeescript gem, because I think coffee -> jsx -> javascript would end up being kind of a mess. This hasn't caused any dependency problems for me, but not 100% sure on this one, so just let me know if this messes anything up.

React and Foundation  should "just work" after you install the gems
Oh oops I forgot git doesn't track empty directories, there should be a directory called `app/assets/javascripts/application`. I did this so we can put all the non-react js stuff in there, and then react components in a separate `app/assets/javascripts/react-components` so we don't compile the react files into the main `application.js`. I can add an empty file in the `application/` directory if you want me to?