workflows: object workflow API addition

* Adds new BibWorkflowObject bound methods to start and continue
  workflows for easier integration with the workflows module when
  pre-creating objects.

* Adds new tests for the new methods.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
deposit: workflow integration changes

* Updates the Deposition and DepositionType classes to use
  newer workflows object bound API.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>