More request validations

[judgej]

We need to make sure we can catch all data validation errors before it reaches the bank API, just for robustness and to keep the remote bank API logs cleaner. This list would be good:

• [x] UUIDs - lower-case UUID4 seems to be the convention here
• [ ] Mandatory/optional fields
• [x] Numeric/integer
• [x] String min/max length
• [x] Regular expression, with some common ones:
  • [x] Reference
  • [x] Payee name
  • [x] Account description

[judgej]

The setting of accountUid, addressUid and paymentUid can be moved to the AbstractRequest to remove a fair number of duplications.