Add a status bar line to the table.

        This function returns the status bar and it can be modified
        from this return value.

def add_status_line(self, label):
        """Add a status bar line to the table.

        This function returns the status bar and it can be modified
        from this return value.
        """
        status_line = StatusBar(label,
                                self._sep_start, self._sep_end,
                                self._fill_char)
        self._lines.append(status_line)
        return status_line