Extend DM4 to DMX Content Migration Functionality

The previously developed generic ex- and import facility where constrained to a specific use-case. The new usecases require more fine-grained ex and import.

DM4 Export:

• Include topic level workspace assignments

DMx Import:

• Recreate Workspaces with new Ownership and Default Sharing Mode (Collaborative)
• Re-create topic-level workspace assignments
• Map dmx.webbrowser.webpage topic, too