function Breadcrumb(containerGroup) {
    /**
     * @private
     * @type {module:zrender/container/Group}
     */
    this.group = new Group();

    containerGroup.add(this.group);
}
Caution: a el can only be added once, otherwise 'done'
might not be called. This method checks this (by el.id),
suppresses adding and returns false when existing el found.

@param {modele:zrender/Element} el
@param {Object} target
@param {number} [time=500]
@param {number} [delay=0]
@param {string} [easing='linear']
@return {boolean} Whether adding succeeded.

@example
    add(el, target, time, delay, easing);
    add(el, target, time, easing);
    add(el, target, time);
    add(el, target);