HG-207 Disable debugging for production env

https://wikia-inc.atlassian.net/browse/HG-207
Export environment variable to front end and use it to turn debugging off or on. Allow to override it with querystring `?debug=1`.
It's supposed to switch out the versions of ember to ember.prod.js, which removes a bunch of assert statements and other things useful only to development. Why can't we use ember.prod.js now?