Simplify pay page

- [x] Ready to merge
- Reduce options on the page (single checkbox for "business" instead of "Are you - biz or individual")
- Hide business details by default
- Use same blue call to action buttons as the help site

![screen shot 2014-08-01 at 13 09 35](https://cloud.githubusercontent.com/assets/13700/3778526/cf3d11c8-1974-11e4-923b-d34df6e969f1.png)