SceneTreeWidget: Disable sorting while RemoveCommands are executing. This speeds up removal significantly for large scenes.
Add Entity::HasParent() so shared_ptr is not created and returned to know this state.
Scene: CreateContentFromXml/Binary/SceneDesc() Implement pre-signaling sorting of created Entities to alleviate parent detection complexity and use ParentingTracker in all versions. New public API: EntityParentId(), SortEntities(). New private utility functions to do sorting and parent detection in a common place, no more copy paste of logic all around the class.