nullptr checks for Hammer.ActiveMap MapEntity / MapMesh constructors will default to active map doc if not specified MapView wraps CMapView so we can use it in addon space Add `[CanDrop( string AssetFileExtension )]` that support `IMapViewDropTarget.DragEnter( Asset ... )`, make it all accessible to addon space Move MaterialDropTarget to addon space Hammer: Add SoundDropTarget - creates snd_event_point for .sound assets