[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.
It seemed to be a bug with jshint's globbing - that glob says "exclude everything but `app` and `lib`", but jshint was including vendor for some reason too, so I added that rule there. jscs didn't have that issue.