Get app config from service

Having [our config](https://github.com/guardian/media-service/blob/master/kahuna/public/js/app.js#L27) come [from Play](https://github.com/guardian/media-service/blob/master/kahuna/app/views/main.scala.html#L10) is not a great dependency.

There is a [good discussion going on about it](http://stackoverflow.com/questions/16286605/initialize-angularjs-service-with-asynchronous-data) with a few solutions / hacks.