Remove wrapping div from backbone view for folders list

Fixes a minor issue stumbled upon while investigating #341 
(does not fix that issue though)

* Before :
![screenshot from 2014-09-21 23 46 52](https://cloud.githubusercontent.com/assets/8377141/4361993/6159c73a-4289-11e4-8515-9635fd6bb0ba.png)

* After :
![after](https://cloud.githubusercontent.com/assets/8377141/4361990/5f0be206-4289-11e4-99ae-fcc9077e6f6c.png)


thanks @DeepDiver1975 for the instructions