Analytics: Send an event for page changes

This is not perfect as we do not get an event for the first page.

https://github.com/flutter/flutter/issues/19249

lib/analytics.dart

@@ -0,0 +1,7 @@
+import 'package:journal/app.dart';
+
+import 'package:firebase_analytics/firebase_analytics.dart';
+
+FirebaseAnalytics getAnalytics() {
+  return JournalApp.analytics;
+}

lib/app.dart

@@ -18,7 +18,7 @@ class JournalApp extends StatelessWidget {
     var onBoardingDone = stateContainer.appState.onBoardingCompleted;
     var markOnBoardingCompleted = () {
       stateContainer.completeOnBoarding();
-      analytics.logEvent(name: "on_boarding_complete");
+      analytics.logEvent(name: "onboarding_complete");
     };
     var home = onBoardingDone
         ? new HomeScreen()

lib/screens/onboarding_screens.dart

@@ -6,6 +6,7 @@ import 'package:shared_preferences/shared_preferences.dart';
 
 import 'package:path/path.dart' as p;
 
+import 'package:journal/analytics.dart';
 import 'package:journal/state_container.dart';
 import 'package:journal/storage/git.dart';
 
@@ -76,6 +77,30 @@ class OnBoardingScreenState extends State<OnBoardingScreen> {
         }
       },
       itemCount: pageCount,
+      onPageChanged: (int pageNum) {
+        print("PageView onPageChanged: " + pageNum.toString());
+        String pageName = "";
+        switch (pageNum) {
+          case 0:
+            pageName = "OnBoardingGitUrl";
+            break;
+
+          case 1:
+            pageName = "OnBoardingSshKey";
+            break;
+
+          case 2:
+            pageName = "OnBoardingGitClone";
+            break;
+        }
+        getAnalytics().logEvent(
+          name: "onboarding_page_changed",
+          parameters: <String, dynamic>{
+            'page_num': pageNum,
+            'page_name': pageName,
+          },
+        );
+      },
     );
 
     return new Scaffold(