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
 
`PMT-1000` is in here twice, and it's weird to see it listed in both success and error codes.