Check CoffeeScript using CoffeeLint

At my company we have quite a lot of CoffeeScript code, and I would love for Hound to be able to check CoffeeScript code too, not just Ruby. The current implementation only checks four rules, however if more rules are added to CoffeeLint they should be fairly straight-forward to add to Hound. The implementation does support customization through a `coffeelint.json` file, though.

TODO:
- [x] Update `app/views/application/configuration.haml`?
I broke that line in 9fc321904ce8a0d5ac6a26eae0c679613c615948 and forgot to join it up again in 8a5a34d554cc8337ebbb52f2876e661dff333ca7.