JBPM-3785: Exception handling

This code is to show Kris and Maciej (and others) what I've written so for for exception-handling. 

What still needs to be done is the marshalling side: currently, not all nodeInstances can be marshalled, which means that processes with an active nodeInstance (that threw the exception) that is not a container/foreach node will cause errors upon marshalling. The fix for this is simply to add support for those nodes in marshalling. 

Please see the related drools pull-request for the framework/mechanism.