This macro enables/disables a menu item of a default menu (like File, Edit,...)
or an added menu (toolbox menu) of the main Scilab panel (Console).
Indeed it is not easy to get the handle of menus of the Scilab Console panel.
Also the 'enable' property does desactivate a menu item but does not mask it.
This function uses tricks to do all these.
Given the menu label and the menu item label, it searches for the menu item in
all menus (but it does not take in account sub menus), and enables/disables it.
