Fix issuing and termination of requests

The functionality is missing that leads to our final statet 'terminated' for notarization requests.

ATM - we end in "accepted" state where we call the issue-api-endpoint to issue the credential. As discussed with @neil.crossley, we cann listen for a RabbitMQ-message which tells us that a credential has been issued. On this event we will set the request to its final state 'terminated'.

@tsabolov: To associated the event on the rabbitMQ-channel and the session, we need its ID. I plan to add a parameter to our call to your api containing it. This id would then have to be sent back to us when the corresponding credential is issued. Woud this be possible?

@neil.crossley pls - correct me if i'm wrong ;)