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

Manuall porting https://github.com/Activiti/Activiti/commit/a556eced74f95d1faf37ef812c39210f1e44db02 to v6

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

- Support for subclasses (eg Timer/Message > Job)  when doing a getList on the cache

Uses the BulkCheckedDeleteOperations which does a bulk delete, but with optimistic locking check.

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

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

Fix process deletion, consolidating process delete methods in ExecutionEntityManager (still needs some love probably)

Setting process instance id to process instance execution (was the same in v5). Fixing outfall of that