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.
As a big fan of grunt, would be happy to do it!