When a click is registered on the plot, appends the click location to self.peak_vals and plots a red dot in the
        click location
        :param mouse_event: a mouse event object for the click

def plot_clicked(self, mouse_event):
        """
        When a click is registered on the plot, appends the click location to self.peak_vals and plots a red dot in the
        click location
        :param mouse_event: a mouse event object for the click
        """
        if type(self.peak_vals) is list:
            self.peak_vals.append([mouse_event.xdata, mouse_event.ydata])
            axes = self.matplotlibwidget.axes
            # can't use patches, as they use data coordinates for radius but this is a high aspect ratio plot so the
            # circle was extremely stretched
            axes.plot(mouse_event.xdata, mouse_event.ydata, 'ro', markersize = 5)

            # axes.text(mouse_event.xdata, mouse_event.ydata, '{:d}'.format(len(self.peak_vals[-1])),
            #                  horizontalalignment='center',
            #                  verticalalignment='center',
            #                  color='black'
            #                  )
            self.matplotlibwidget.draw()