Set a label for the y-axis of a subplot.

        :param row,column: specify the subplot.
        :param text: text of the label.

def set_subplot_ylabel(self, row, column, text):
        """Set a label for the y-axis of a subplot.

        :param row,column: specify the subplot.
        :param text: text of the label.

        """
        subplot = self.get_subplot_at(row, column)
        subplot.set_ylabel(text)