More on Orders and Donations add Payments and Docdata

- Remove migrations for donations, orders and payments
- Remove payments_adyen and payments_mollie
- Add the first API tests for donations & orders
- Add API endpoint to get (public) project donations
- Add a basic Fundraiser app so that can be used easily in Bb implementations
- Add simple functions and abstract class with unimplemented (static) methods in payments adapters
- Rename en restructure some payment models to follow design decisions
- Add payment serializer
- Adjust Ember payment js to fit the new API
- Add first draft of payment API views
- Add first draft of payments_docdata adapter and separate interface (remove lot's of old code)
- Add empty classes to payments_mock
- Add some Ember front end for payments_mock
- Use basic implementation apps for Donation, Order & Fundraiser in Bb test suite


Why a method full_clean? Do you need to call the three steps of validating a model for this class?