legendItemClass (legendItemClass) {
        if (!arguments.length) {
            return this._legendItemClass;
        }
        this._legendItemClass = legendItemClass;
        return this;
    }
This can be optionally used to override class for legenditem and just use this class style.
This is helpful for overriding the style of a particular chart rather than overriding
the style for all charts.

Setting this will disable the highlighting of selected items also.
@param {String} [legendItemClass]
@return {String|HtmlLegend}