ISIS-960: Make the event bus handle exceptions more gracefully, not swallow them.
ISIS-960: handle exception for subscriber when invoked no-arg action.  More robust exception handler strategy.

If a no-arg action is invoked which generates an exception in a subscriber, then the Wicket UI should detect this and re-render the original object with any messages generated.

In addition, the exception handler strategy previously would only abort the transcation if a NonRecoverableException or a RecoverableException was thrown.  This is too narrow; should abort the transaction for any exception thrown