fix issues

- fix Sector group no-successive issue when saving as nmo
- add nong ventilator adder.
- use copy.copy to write some code to reduce the calling of get/set_raw_vt_mtl()
- keep texture when apply virtools mtl preset.

bbp_ng/PROP_virtools_group.py

@@ -270,7 +270,7 @@ class SharedGroupNameInputProperties():
     )
     
     def draw_group_name_input(self, layout: bpy.types.UILayout) -> None:
-        layout.prop(self, 'group_name_source', expand=True)
+        layout.prop(self, 'group_name_source', expand = True)
         if (self.group_name_source == 'CUSTOM'):
             layout.prop(self, 'custom_group_name')
         else: