Add optional controller key `requireLogin`.

This PR does the following stuff:

- Adding this key will redirect a user that isn't logged in to the login site rather then the site they requested.
- Added the previously described key to the event.create controller so that un-logged-in users cannot access it directly.
- Add in functionality in navbar to hide menu item.
- Closes #32.

cc/ @snorrid 
Is there any difference to using [authenticated](https://github.com/tviund/sciencetrip_signup/blob/master/client/app/account/account.js#L16) ?