Wrap analytics code in GOVUK interface

Wraps our analytics code in a stripped down
version of GOVUK.Analytics to allow us to plug in
the GOVUK code for consent.

app/assets/javascripts/analytics/init.js

@@ -0,0 +1,39 @@
+(function (window) {
+  "use strict";
+
+  window.GOVUK = window.GOVUK || {};
+
+  const trackingId = 'UA-26179049-1';
+
+  // Disable analytics by default
+  window[`ga-disable-${trackingId}`] = true;
+
+  const initAnalytics = function () {
+
+    // guard against being called more than once
+    if (!('analytics' in window.GOVUK)) {
+
+      window[`ga-disable-${trackingId}`] = false;
+
+      // Load Google Analytics libraries
+      window.GOVUK.Analytics.load();
+
+      // Configure profiles and make interface public
+      // for custom dimensions, virtual pageviews and events
+      window.GOVUK.analytics = new GOVUK.Analytics({
+        trackingId: trackingId,
+        cookieDomain: 'auto',
+        anonymizeIp: true,
+        displayFeaturesTask: null,
+        transport: 'beacon'
+      });
+
+      // Track initial pageview
+      window.GOVUK.analytics.trackPageview();
+
+    }
+
+  };
+
+  window.GOVUK.initAnalytics = initAnalytics;
+})(window);