Introduce concept of sub-departments

This feature introduces child departments. Departments can now have parents and children, which allows for a system which more closely corresponds to larger organizations department layouts. Department access is cascaded so that members of parent departments automatically have access to all child departments. 

This also allows for more creative approaches to the access control system where department hierarchy might be organized by something like location.

### Outstanding
  * [ ] Cascade dashboard statistics
  * [ ] Ensure dashboard statistics are accurate for nested departments

### Screenshot Tour

##### Specify a parent department
![screen shot 2014-11-13 at 2 05 53 pm](https://cloud.githubusercontent.com/assets/672074/5036789/6334493a-6b48-11e4-94f5-638abd0ad491.png)

##### Full department path shows up
![screen shot 2014-11-13 at 2 07 05 pm](https://cloud.githubusercontent.com/assets/672074/5036812/8ca6cac2-6b48-11e4-8419-14769a10d5cf.png)

![screen shot 2014-11-13 at 2 07 20 pm](https://cloud.githubusercontent.com/assets/672074/5036830/a8d0e5b6-6b48-11e4-85c3-4f9402df5f8e.png)