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.
" For mysterious reasons, some tests consistently fail only on PhantomJS. Therefore, as a team we decided not to use PhantomJS to run the tests." Oddly enough, that sounds very familiar to me. 

The decision makes sense. Just a quick suggestion though. Have you considered using only one karma file and override the browser from Gruntfile? It would avoid redundancy.