Multi instance refactoring: introduced the 'IS_MI_ROOT_' column to indicate an execution is the root of a multi instance. Every multi instance (sequential and parallel, parallel already had it) will now spawn an execution that acts as parent for the whole multi instance. This has two benefits: cleanup becomes way easier and it opens up the possibility to dynamically add new instances to a multi instance (not yet implemented).

Massively Cleanup Up TaskEntity: making it what it should be, a container for data and not a central hub for all kinds of operations (slightly overreacted).

Refactored all entity classes: added an interface for each entity, such that alternative data stores can swap out the entity objects with more fitting ones (eg with annotations like Neo4j, JPA, etc or other mechanisms. Internally, only the entity interface is used)

Making entity manager interfaces consistent: removing duplicate methods (findById/getEntity/..) and make sure they pass the entity cache

(work in progress) Moving logic from entities into EntityManager classes. Removing unneeded methods and consolidating almost similar logic.

Breaking change:  org.activiti.engine.impl.pvm.delegate; (ActivityBehavior and others) changed to  org.activiti.engine.impl.delegate;

Merging https://github.com/Activiti/Activiti/commit/fe7e23d0cff8bd7c312040929cfd11ba434fc17a + fixing for v6

Initializing fields to 0, null, or false is not needed and just duplicates work.

Changes for multiple VariableInstance insertions in one query

Remove an extra statement

Added bulk insert for UserEntity

Changes in all entities for bulk insert

Added Oracle specific bulk insert queries

Resolve Test Issues

ACT-4014 Changes for maintaining dependency ordering for entities while inserting

Fixing the FullHistoryTest: refactoring the way HistoricActivityInstances are looked up (still needs to be moved to the entity manager), creating one if one is not found (to solve the order problem).

Fixing a nasty child deletion cleanup use case with terminate end event - switched to using ExecutionTree approach with bfs iterator - probably overkill for now, but will make sense once we start caching executions

This allows schedule *or not* a BoundaryTimer Job, depending on dueDate
execution variable value : if null - just ignoring BoundaryTimer.

Format back to 2 spaces for now, merging back from Activiti 5 is really an issue with spacing differences

- removed BpmnModelCache, and made the BpmnModel part of the procesDefinitionCache
- Introduced ProcessDefinitionUtil, which should be the basis for all things needed a Process definition (entity or BpmnModel counterpart)

- Renamed behaviour to behavior (consistent with ActivityBehavior)