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

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)