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.
@vilmosioo Thanks for the recommendation. For mysterious reasons, some tests consistently fail only on PhantomJS. Therefore, as a team we decided not to use PhantomJS to run the tests. 

The travis CI build uses https://saucelabs.com to run the unit tests in a browser since we don't want to use PhantomJS. We want to limit the use of sauce to our CI builds since we are on a free plan and have limited access. Therefore, there is a local config for running the build locally using your installed version of Chrome.