function addListener(element, listener) {
        var id = idHandler.get(element);

        if(!eventListeners[id]) {
            eventListeners[id] = [];
        }

        eventListeners[id].push(listener);
    }
Stores the given listener for the given element. Will not actually add the listener to the element.
@public
@param {element} element The element that should have the listener added.
@param {function} listener The callback that the element has added.