Track event when someone previews basic view

We’re interested to know which services are looking at the basic view
preview (even if they’re not turning it on).

This commit logs their service IDs as events into Google Analytics.

app/assets/javascripts/analytics.js

@@ -0,0 +1,32 @@
+(function(Modules) {
+  "use strict";
+
+  if (!ga) return;
+
+  function sendEvent(category, action, label) {
+
+    ga('send', 'event', category, action, label);
+
+  }
+
+  Modules.TrackError = function() {
+
+    this.start = component => sendEvent(
+      'Error',
+      $(component).data('error-type'),
+      $(component).data('error-label')
+    );
+
+  };
+
+  Modules.TrackEvent = function() {
+
+    this.start = component => sendEvent(
+      $(component).data('event-category'),
+      $(component).data('event-action'),
+      $(component).data('event-label')
+    );
+
+  };
+
+})(window.GOVUK.Modules);

app/assets/javascripts/errorTracking.js

@@ -1,22 +0,0 @@
-(function(Modules) {
-  "use strict";
-
-  Modules.TrackError = function() {
-
-    this.start = function(component) {
-
-      if (!ga) return;
-
-      ga(
-        'send',
-        'event',
-        'Error',
-        $(component).data('error-type'),
-        $(component).data('error-label')
-      );
-
-    };
-
-  };
-
-})(window.GOVUK.Modules);