Revision 618686

Hooked most of FONode into the new event mechanism. The FOUserAgent provides a DefaultEventBroadcaster instance.
If a producer method declares throwing an exception, the event is automatically marked FATAL and the dynamic proxy throws an exception right after notifying the listeners.
The exceptions are created through the EventExceptionManager. It currently contains only one exception factory for ValidationException. If we need more such factories it's better to register them dynamically. Right now, they're hard-coded.