Grouping memberships

Memberships are now sorted and grouped (grouped on the department page). On the department page it gives you tabs that let you filter down by the team.

![screen shot 2014-08-28 at 4 10 37 pm](https://cloud.githubusercontent.com/assets/957859/4084394/9a336438-2f08-11e4-82bd-83101790d23d.png)