Adding detail to transaction type definition

[MichaelJBRichards]

TIPS needs to be able to analyse use cases by recipient type as well as by initiator type: for instance, to be able to distinguish readilybetween P2P, P2B and P2G use cases. We therefore propose to add a field to the TransactionType object (spec Section 7.4.18.)

The field should be called recipientType. It should be optional to support backwards compatibility. It should have the same type as the initiatorType field in the current data structure.