Cmmn: fix end time of historic task not always set + identitylinks not cleaned up after test + sql server upgrade fix

Add subscope identifier for variables to mimic variable storage for executions in the same way for cmmn planitem instance and case instance

Added CaseInstance, PlanItemInstance and MilestoneInstance (similar to process engine concepts) and basic agenda operation to activate plan items of case model.

- basic maven module setup (similar to dmn: api/model/converter/engine/configurator)
- Moved around classes that were duplicated between engines to the common module and packages
- model and converter classes to parse simple test .cmmn file
- Basic setup of resource, deployment and definition entities (similar to bpmn/dmn)
- cmmn parser that adds behavior to plan items (currently not doing anything)
- Docs/javadocs currently not added, will be added in the future