Book 713 Docdata payment adapter

- Implement PaymentService
- Change DocdataPaymentAdapter to new architecture.
- Add simple donation admin.
- Put Order/donation statuses inside model so we can reference it (get_order_model) and override it if we need another implementation.
- add fundraiser to donations api
- update ember to use OrderPayment rather than Payment to match API
- fix error reloading order before transitioning to PSP
- correctly load project or fundraiser when returing from PSP
- add test for fundraiser donation and make fundraiser field not required for donation
DONATION_MODEL = get_donation_model()
Better this one so no need for string isn't it?