[#1975] Tidy Public Body Category Management UI

- Fixes #1975
- Tidy the UI and make it more uniform with other admin screens

**-**

![screen shot 2014-11-19 at 14 50 36](https://cloud.githubusercontent.com/assets/282788/5107701/d4fe6066-6ffb-11e4-920f-2b7fc2444a33.png)

**+**

![screen shot 2014-11-19 at 14 50 51](https://cloud.githubusercontent.com/assets/282788/5107704/d9b49724-6ffb-11e4-8afe-7693b320c4fb.png)