Updated course homepage layout so question headers sit on top of content on small screens.

Previous:
![previous](https://cloud.githubusercontent.com/assets/5265058/5531797/b53626d0-89fd-11e4-815c-362e5bc43b9d.png)

Updated:
![screen shot 2014-12-22 at 5 05 51 pm](https://cloud.githubusercontent.com/assets/5265058/5531804/c3a89c66-89fd-11e4-9b5f-7816fbfa041b.png)

![screen shot 2014-12-22 at 5 05 39 pm](https://cloud.githubusercontent.com/assets/5265058/5531806/c6d1c84a-89fd-11e4-95e7-45a66c90865f.png)

@rocha @clintonb