QuickBooks Payments 

WIP to integrate QuickBooks Payments.

Basic integration is complete, items remaining:
- [x] update integration to calculate OAuth signature given all token credentials
- [ ] remote tests for Quickbooks 
- [ ] unit tests 
- [x] implement some pattern for generating a GUID
 
to answer your question more directly, It wasn't clear to me which error it mapped to best, because ``` incorrect_cvv ``` seemed a little strong, but i'll change it to that, and for the others too.