Deleting a probe in the editor now automatically does a cleanup of it's baked cubemap files

Also added it to do the prefilter/irrad processing on any StaticCubemap selected.

Engine/source/gui/worldEditor/undoActions.cpp

@@ -155,6 +155,9 @@ void MEDeleteUndoAction::deleteObject( SimObject *object )
    if ( group )
       state.groupId = group->getId();
 
+   //Do any special handling of delete actions the object may do
+   object->handleDeleteAction();
+
    // Now delete the object.
    object->deleteObject();
 }