Manage with less JS

:fork_and_knife: I think if we're going to take the UJS approach with our JS interactions we should also take advantage of RJS and let the server handle much of the template rendering. This greatly reduces the amount of spaghetti jQuery code by rendering `update.js.erb` and either rendering the updated cookbook urls into the `.cookbook-urls` div or rendering an error message. This also has a nice side effect of letting us take advantage of l18n for success/failure messages. Additionally this adds abide so the URL validation is handled on the client side with server side validation as a fallback.