yAxisOnClick (handler) {
        if (!arguments.length) {
            return this._yAxisOnClick;
        }
        this._yAxisOnClick = handler;
        return this;
    }
Gets or sets the handler that fires when a row tick is clicked in the y axis.
By default, if any cells in the row are unselected, the whole row will be selected,
otherwise the whole row will be unselected.
@param  {Function} [handler]
@returns {Function|HeatMap}