Redirect users when they visit the homepage while not logged in

When users visit the app homepage while not logged in, they see a sad white screen. Let's redirect them to the login to make life easier. Anonymous users browsing surveys will not be effected. 

Looks like this right now:
![2014-09-08 05 24 29 pm](https://cloud.githubusercontent.com/assets/86435/4193082/a08a4ac4-379e-11e4-822f-8365371b8083.png)

Will look like this:

![2014-09-08 05 25 40 pm](https://cloud.githubusercontent.com/assets/86435/4193094/af999240-379e-11e4-81b6-63d6954a01d0.png)