yAxisLabel (labelText, padding) {
        if (!arguments.length) {
            return this._yAxisLabel;
        }
        this._yAxisLabel = labelText;
        this.margins().left -= this._yAxisLabelPadding;
        this._yAxisLabelPadding = (padding === undefined) ? DEFAULT_AXIS_LABEL_PADDING : padding;
        this.margins().left += this._yAxisLabelPadding;
        return this;
    }
Set or get the y axis label. If setting the label, you may optionally include additional padding
to the margin to make room for the label. By default the padding is set to 12 to accommodate the
text height.
@param {String} [labelText]
@param {Number} [padding=12]
@returns {String|CoordinateGridMixin}