Forbid access to some features for non beta users

![screen shot 2014-10-14 at 10 26 19 pm](https://cloud.githubusercontent.com/assets/667753/4639304/53b72428-540a-11e4-80fc-7839ab4ce50e.png)

Implements #712.
I'm not sure if this is the right place for it.
Should all the show actions be restricted? Even the user profile page?