LPS-41340 Apply changes to BaseStagedModelDataHandler - entity associated categories should be exported and imported
LPS-41340 Apply changes to Layout/PortletExporter and PortletImporter - exporting and importing of asset categories will be handled by new SMDHs
LPS-41340 Update test for the new infrastucture - not much change since we were already testing asset entries and categories, just needed a small alignment