Added a list of received messages to the Subscriber test class
Added a test that checks subscriber was able to retrieve all messages published by the publisher. Fails now, because the ClaimService is yet to be implemented.
Implemented a so-called claim service. When a client requests the next message to its mailbox, the mailbox forwards the request to the bus. The bus has a thread waiting for claims. It retrieves claimed messages, removes them, and sends them to the requester.
Added Claim and Filter