Save donor info

First draft of saving donor info.

1. Creates a new application to store pay.gov-related functions - this division should allow us to limit which urls are accessible simply by turning applications on and off
2. Move payxml and several related functions from the view code into the new app
3. Save the generated xml when a user hits the confirmation page
4. Remove some unneeded fields from the review submission form
Hmm. Do we want to remove this out of the base setting? Putting it here means it gets included on all servers. Maybe there's a copy of the production settings for paygov servers?