Hide interactive section header on mobile

### Before

![screen shot 2014-05-12 at 16 40 45](https://cloud.githubusercontent.com/assets/85783/2946468/184b0640-d9ec-11e3-96b8-5cd13f3fa32d.PNG)


### After

![screen shot 2014-05-12 at 16 40 34](https://cloud.githubusercontent.com/assets/85783/2946469/1ba5b8e4-d9ec-11e3-95b0-5bf1b7bccd4e.PNG)


![the-internet](https://cloud.githubusercontent.com/assets/85783/2946476/2d8fe534-d9ec-11e3-8af7-d63bdd1134d1.gif)