* Added support for outbound DecisionGateway within engine selection.
* Function rebuild_gateways now pre-compiles and marshals python code suitable for engine eval().
* Added catalog_2 to librarian test library.
* Added mock workflow to test DecisionGateway routing logic.
* Refactored librarian to remove a workflow from the parent catalog should it fail to fully build.
* Sessions have stub support for parent <-> child relationships.