Re-think checked SerializationException

[niloc132]

In the old API, this was a checked exception, so you had to catch it, but then caught and handed to AsyncCallback.onFailure or serialized it and sent it to the client. Currently the new implementation is catching it and converting it to an IllegalStateException, which is also lame, but for handling messages traveling either direction, we're a little limited without guaranteeing that the caller has specified a callback. Additionally, since serialization is uncoupled from the endpoint wiring, there isn't a guarantee that the other side will be generated anyway.

Some options (not exhaustive, might be helpful to use more than one):

• Make it a runtime exception
• Allow @SerializationWiring-annotated types to declare this as a throws and avoid try/catch wrap
• Endpoints should explicitly catch this and route to local onError when reading, and just throw back out to calling code when writing