MENU
- the entries in menudata.xml and module_tree_menudata.xml are autogenerated 
  via tools/build_modules_xml.py (see ../Makefile)
- Find more info at
  https://grass.osgeo.org/grass-devel/manuals/wxGUI.toolboxes.html
  (../docs/wxgui_sphinx/src/)
- additionally
  https://trac.osgeo.org/grass/wiki/wxGUIDevelopment/Toolboxes