zoom out 1 level, or to full data range

def unzoom(self, event=None, set_bounds=True):
        """ zoom out 1 level, or to full data range """
        lims = None
        if len(self.conf.zoom_lims) > 1:
            lims = self.conf.zoom_lims.pop()
        ax = self.axes
        if lims is None: # auto scale
            self.conf.zoom_lims = [None]
            xmin, xmax, ymin, ymax = self.data_range
            lims = {self.axes: [xmin, xmax, ymin, ymax]}
        self.set_viewlimits()
        self.canvas.draw()