Task: Define outbound message event structure

[dbluhm]

Figure out how much information is required alongside the packed message for the outbound message delivery to deliver the message correctly. This structure will be included in the outbound message event payload.

[burdettadam]

I propose we make a QueuedOutboundMessage class that extends Event from eventBus and implements QueuedOutboundMessage class. Currently The event class has a payload and topic. The QueuedOutboundMessages have a few more attributes used for routing. With events of this kind, we can easily drop in the notify and subscribe interface where needed. This also gives us room to change if we learn something needs to be different.

[dbluhm]

openwallet-foundation#1286