Changes to donation form, plus a simple donation review page

This is a larger pull request than I would normally submit. Mostly, I forgot there were all these changes. 

This adds some missing fields to the donation form, and makes an attempt to break apart individuals and organizations. I'm sure in the future those two entities will see different fields too. 

Happy to answer questions, and look forward to the code review. 


Try: https://github.com/18F/peacecorps-site/pull/5