Escalation improvements

- the cancelActivity attribute (per the *spec*, but not per the xsd) defaults to "false"!
- escalations are referenced by their "escalationCode" attr values
- exceptions thrown when syntax is incorrect (no escalationRef in escalation end event)
JBPM-3785 JBPM-4052: Compensation execution
JBPM-3785 JBPM-4052: Compensation parsing
JBPM-3785 JBPM-4052: Compensation tests
Seperating intermediate escalation, compensation and error tests into their own class