Save all figure in dirname.

def save_all_figures_todir(self, dirname):
        """Save all figure in dirname."""
        fignames = []
        for thumbnail in self._thumbnails:
            fig = thumbnail.canvas.fig
            fmt = thumbnail.canvas.fmt
            fext = {'image/png': '.png',
                    'image/jpeg': '.jpg',
                    'image/svg+xml': '.svg'}[fmt]

            figname = get_unique_figname(dirname, 'Figure', fext)
            save_figure_tofile(fig, fmt, figname)
            fignames.append(figname)
        return fignames