Support Deferred transaction type and abort/release instructions

[judgej]

New updates to the gateway API:

20-01-2017 v1 Added Deferred transaction type and abort \ release instructions.

• [x] Deferred transaction type
• [x] abort instruction
• [x] release instruction
• [x] instructions message - get a list of instructions for a transaction (a GET instruction without an instructionType)
  • [x] Abstract the instruction response classes.
  • [x] Abstract the collection functionality, since we now have two collections.

[judgej]

The fetch instructions response is an array of instructions and timestampes, or a 404 if there are none. These are the instructions that have been applied to the transaction. It's not clear whether those instructions will ever get a state that can be tracked.

[judgej]

Added an Instruction Collection response object. This has highlighted two things:

• With an instruction collection and an error collection, we should now extract the collection. Not sure if traits or an abstract class is the way to go. Edit: I guess a trait will be more flexible, so a collection can be applied to requests, responses and other non-message contexts. However, most examples of collections are data agnostic, while these collections are for specific abstract class types only.
• The Abort/Release instructions both extend the Void instruction, for nothing more than legacy reasons. Abstract the instruction response to make it easier to pass around.

[judgej]

Do we need separate Void/Abort/Release instruction responses? THey all contain the same standard type and date properties, so are identical, and even if not, could self-identify their instruction type. Maybe just one Instruction class will be enough, for now at least.