Add Bower for front end package management.

Since Bower is typically used for front end package management, and some of the dependencies I want to use (Ember, Bootstrap) aren't published to npm, I added Bower and moved all of the front end dependencies over to it. I also added an script that automatically runs `bower install` after `npm install` so installing the project still works the same.

This question on StackOverflow covers this topic: http://stackoverflow.com/questions/14166591/automate-npm-and-bower-install-with-grunt

We could also run both `npm install` and `bower install` with Grunt, which might be an alternative to the post-`npm-install` script that's worth discussing. cc/ @pushred @joanniclaborde