Plot groups of GOs which have been placed in sections.

def plot_sections(self, fout_dir=".", **kws_usr):
        """Plot groups of GOs which have been placed in sections."""
        kws_plt, _ = self._get_kws_plt(None, **kws_usr)
        PltGroupedGos(self).plot_sections(fout_dir, **kws_plt)