QuickBooks Payments 

WIP to integrate QuickBooks Payments .

Basic integration is complete, items remaining:
- [ ] update integration to authenticate via OAuth
- [ ] authentication testing 
- [ ] remote tests for Quickbooks 
- [ ] some unit tests 
- [ ] implement some pattern for generating a GUID
 
@girasquid Cool, we'll do that. 
@ntalbott Unfortunately we're dealing with OAuth 1 here. :disappointed: So yes, at this point I have an access token and token secret that's reusable, but each request also requires a signature seeded by a combination of the request's HTTP verb and URL parameters; something I can't know beforehand. Would *love* some Bearer auth here instead.