Introducing 'workflow' as an individual entity

* Added Workflow DB model
* Removed 'workbook_name' parameter from Engine.start_workflow signature
* Fixed unit tests
* Fixed module trusts to create individual workbook entities when
 on workbook definition update
* Fixed API tests
* Switched v1 controllers to explicitly use DB API v1

Change-Id: I6a096e1c5d8082d3d1cdd47b575b85b28224d2a6
Merge "Introducing 'workflow' as an individual entity"