modules/menusystem: add a way to preserve creation order

gamecore/modules/menusystem/parent.lua

@@ -112,6 +112,10 @@ function Menu:getWidgetSize(id)
   return self.widget.w, self.widget.h
 end
 
+function Menu:getWidgetNumber()
+  return #self.widget.list
+end
+
 -- ACTION FUNCTIONS
 -- Send actions to the widgets
 

gamecore/modules/menusystem/widgets/init.lua

@@ -46,6 +46,7 @@ end
 
 function BaseWidget:register()
   self.menu:addWidget(self)
+  self.creationID = self.menu:getWidgetNumber()
 end
 
 function BaseWidget:redrawCanvas()