Remove thumbnail.

def remove_thumbnail(self, thumbnail):
        """Remove thumbnail."""
        if thumbnail in self._thumbnails:
            index = self._thumbnails.index(thumbnail)
            self._thumbnails.remove(thumbnail)
        self.layout().removeWidget(thumbnail)
        thumbnail.deleteLater()
        thumbnail.sig_canvas_clicked.disconnect()
        thumbnail.sig_remove_figure.disconnect()
        thumbnail.sig_save_figure.disconnect()

        # Select a new thumbnail if any :
        if thumbnail == self.current_thumbnail:
            if len(self._thumbnails) > 0:
                self.set_current_index(min(index, len(self._thumbnails)-1))
            else:
                self.current_thumbnail = None
                self.figure_viewer.figcanvas.clear_canvas()