Blacken Whitehall admin header

* Bring Whitehall admin header closer inline with other tools using the admin gem
* Include a more prominent environment bar across the top of the window

- [x] Code review
- [x] Product review

Before:
![screen shot 2014-08-11 at 16 46 03](https://cloud.githubusercontent.com/assets/319055/3878381/bbdf8cd0-216e-11e4-81c7-65f4aad29847.png)

After:
![screen shot 2014-08-11 at 16 46 33](https://cloud.githubusercontent.com/assets/319055/3878382/bbe302b6-216e-11e4-8455-8df1aec1093b.png)