[JavaScript] common

更新craeteElement，自動將建立的元件加入到parent。
===
var common = {};
common.createElement = function (tag, attributes, parent) {
    var element = document.createElement(tag);
    for (var attribute of attributes) {
        element.setAttribute(attribute, attributes[attribute]);
    }
    if (parent !== undefined) {
        parent.appendChild(element);
    }
    return element;
};
===.