Migrates the build from Rake to grunt

Note: I originally set out to encrypt our credentials for Sauce in this repo and the viewer repo but it was causing me problems so I dropped it. I don't think anyone would be too motivated to use the credentials since we only have the free plan available to anyone. If it becomes a problem later we can invalidate the access key and look at encrypting it then.
Yes, the browser config is less straightforward for using sauce and I didn't want to spend a lot of time trying to make it work. If you're interested in doing this. I would be happy to accept a pull request (after this one is merged)