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`.
if we want to be consistent I'd go with `prod`. it's consistent with `dev` instead of `devbox` and will be consistent with `/etc/environment` on our machines.