code: function addGroup(param, cfg) {
      var canvas = this.get('canvas');
      var rst = void 0;
      cfg = Util.merge({}, cfg);
      if (Util.isFunction(param)) {
        if (cfg) {
          cfg.canvas = canvas;
          cfg.parent = this;
          rst = new param(cfg);
        } else {
          rst = new param({
            canvas: canvas,
            parent: this
          });
        }
        this.add(rst);
      } else if (Util.isObject(param)) {
        param.canvas = canvas;
        rst = new Group(param);
        this.add(rst);
      } else if (param === undefined) {
        rst = new Group();
        this.add(rst);
      } else {
        return false;
      }
      return rst;
    }
docs: 添加图组
  @param  {Function|Object|undefined} param 图组类
  @param  {Object} cfg 配置项
  @return {Object} rst 图组