add missing tracking.js to #128

tracking.js

@@ -0,0 +1,13 @@
+(function () {
+
+function trackUsage(eventname, obj) {
+    //console.log('track', eventname, obj);
+    // implement your own tracking mechanism here
+}
+if (typeof exports !== 'undefined') {
+    module.exports = trackUsage;
+} else {
+    window.trackUsage = trackUsage;
+}
+
+})();