Error propagation and reporting

[AndreaV-Lsi]

• Define custom error codes
• generate errors and propagate them to the subscribers (client or server)
• The subscribers of the server/server must override the "Handle Error" method to catch the specific errors
• If an unknown error leads to an invalid Listener reference the server will now shutdown, because it would then kill possibly working connections to clients, but it will stop accepting definitions of new services by throwing a specific error