implement motd button

modules/topmenu/topmenu.lua

@@ -11,4 +11,8 @@ end
 function TopMenu.destroy()
   topMenu:destroy()
   topMenu = nil
+end
+
+function TopMenu.getButton(id)
+  return topMenu:getChildById(id)
 end

modules/topmenu/topmenu.otui

@@ -37,7 +37,8 @@ TopPanel
     margin.left: 6
     tooltip: Message of the day
     icon: /core_styles/icons/motd.png
-    @onClick:
+    visible: false
+    @onClick: EnterGame.displayMotd()
 
   TopButton
     anchors.top: parent.top