[1075] Add jscs and jshint

Adds and configures the linters [jscs](https://www.npmjs.com/package/jscs) and [jshint](http://jshint.com/). Merging into @orenyk's branch since that seems to make the most sense right now.

Also streamlines `bundle install` since we're now just installing what we need to run tests instead of everything.

FWIW, the Travis build *should* be failing, because both jscs and jshint are failing.
any reason why we're not excluding `vendor` here too? I'm not sure how many JS files are going to be in that directory but it might still help.