When the plot control is toggled, set visibility and hand down source

def on_click_plot_widget(self, event):
        """ When the plot control is toggled, set visibility and hand down source"""
        self.plot.source = self.sources
        self.plot.visible = event.new
        if self.plot.visible:
            self.plot.watchers.append(
                self.select.widget.link(self.plot, value='source'))