Better exception handling -- more

[ccleve]

As a followup to #272,

When CopycatClient sends a request, you can process the response with client.submit(foo) .whenComplete(responseObject, errorObject) -> { // do stuff });

The errorObject doesn't always get populated properly.

If you do not have a method in your StateMachine that handles the Foo class, then the server sends an ERROR response, but the client never reports it in whenComplete().

If you throw a RuntimeException within your StateMachine method, an error does get reported to the client, but errorObject = ApplicationException and the type and message of the original exception are lost.

[kuujo]

This has actually been fixed in Copycat 2.0, at least the issue of not reporting proper exceptions and messages has been. It's not clear yet whether the exceptions should be serialized and sent to the client or just the message. Currently, it's just the message with an ApplicationException. One could argue against serializing actual exceptions since they occur inside servers and not on the client.