return a wx.MenuBar() for the menu

def wx_menu(self):
        '''return a wx.MenuBar() for the menu'''
        from MAVProxy.modules.lib.wx_loader import wx

        menubar = wx.MenuBar()
        for i in range(len(self.items)):
            m = self.items[i]
            menubar.Append(m.wx_menu(), m.name)
        return menubar