JBPM-3785 (Compensation): jbpm-flow modifications

- Added a BroadcastEventTypeFilter in order to be able to broadcast the "Compensate-" event to all
  nodes listening for a "Compensation-*" event
- Modified the RuleFlowProessValidator to accept associated activities to (compensation) boundary
  event nodes
- Modified WorkflowProcessInstanceImpl to deal with compensation events (correctly)
- Modified BoundaryEventNodeInstance to deal with compensation correctly
  - it wasn't possible to use a CompensationBoundaryNode/-Instance because
    1. we provide the node instance in the start method
    2. but we can't "look foward" then, and tell if compensation will be used with the boundary event
- Some small other minor fixes
JBPM-3785 (Compensation): jbpm-bpmn2 modifications

- Added/corrected parsing and xml dumping for
  + Associations
  + isForCompensation attribute
- Made compensation (catch) events use BroadcastEventFilters
- Added lots of checks for compensation parsing
Cleaned up FIXME notes and various small things in jbpm-bpmn2 tests
JBPM-3785 (Compensation): jbpm-bpmn2 tests
JBPM-3785 (Compensation): serialization/protobuf logic for the WorkflowProcessInstanceImpl.completedNodeIds field