chore(maven): add BPMN model API to engine and parent pom

related to #CAM-1857
chore(bpmn-api/deploy): add posibility to deploy a BPMN model instance

related to #CAM-1857
feat(bpmn-api): add access to the BPMN model API from java delegate code

Add an interface to access the current model instance and model
element instance. And implement and test it for the following
combinations:

* task listener user task (start, assignment and end event)
* java delegate on service task
* execution listener:
  * process (start and end event)
  * start event (end event)
  * sequence flow (take event)
  * intermediate catch event (start and end event)
  * gateway (start and end event)
  * user task (start and end event)
  * end event (start event)

As a bonus all test processes were created with the BPMN model API.

related to #CAM-1857