Update to Google Universal Analytics

This is an optimized version of the official Google Universal Analytics snippet, based on http://mathiasbynens.be/notes/async-analytics-snippet#universal-analytics. The only difference is that this version still uses `document.getElementsByTagName('script')[0]` instead of `document.scripts[0]` for Firefox < 9 support.

Unminified, optimized code:

```js
(function(window, document, script, variableName, scriptElement, firstScript) {
  window['GoogleAnalyticsObject'] = variableName;
  window[variableName] || (window[variableName] = function() {
    (window[variableName].q = window[variableName].q || []).push(arguments)
  });
  window[variableName].l = +new Date;
  scriptElement = document.createElement(script);
  firstScript = document.getElementsByTagName(script)[0];
  scriptElement.src = '//www.google-analytics.com/analytics.js';
  firstScript.parentNode.insertBefore(scriptElement, firstScript)
}(window, document, 'script', 'ga'));

ga('create', 'UA-XXXX-Y');
ga('send', 'pageview');
```

Minified:

```js
(function(b,o,i,l,e,r){b.GoogleAnalyticsObject=l;b[l]||(b[l]=function(){(b[l].q=b[l].q||[]).push(arguments)});b[l].l=+new Date;e=o.createElement(i);r=o.getElementsByTagName(i)[0];e.src='//www.google-analytics.com/analytics.js';r.parentNode.insertBefore(e,r)}(window,document,'script','ga'));ga('create','UA-XXXX-Y');ga('send','pageview');
```

Closes #1347 and #1369.