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 believe we should stick with the pattern of using the permissions helper when possible. Today this addition does not do anything but in the future the policy for activities may change and the modal wouldn't be shown.

Give me your reply and I will change on every place you commented if you still think this should be done.