Adding example configuration for google analytics

conf/main.example.json

@@ -2,6 +2,10 @@
     "api": "http://localhost:8000/api/v1/",
     "eventsUrl": "ws://localhost:8888/events",
     "debug": "true",
+    # Google analytics, uncomment if needed
+    "analytics": {
+        "accountId": "XXXXXXXXXXXX"
+    },
     "publicRegisterEnabled": true,
     "feedbackEnabled": true,
     "privacyPolicyUrl": null,