redraw the image

def draw(self, parent, box):
        '''redraw the image'''
        import wx
        from MAVProxy.modules.lib import mp_widgets
        if self.imgpanel is None:
            self.imgpanel = mp_widgets.ImagePanel(parent, self.img())
            box.Add(self.imgpanel, flag=wx.LEFT, border=0)
            box.Layout()