isolate firebase analytics code to one file

This way it'll be easier to remove in the future

lib/analytics.dart

@@ -154,6 +154,15 @@ class Analytics {
     this.enabled = enabled;
     return firebase.setAnalyticsCollectionEnabled(enabled);
   }
+
+  Future<void> setCurrentScreen({@required String screenName}) async {
+    await firebase.setCurrentScreen(screenName: screenName);
+  }
+
+  Future<void> setUserProperty(
+      {@required String name, @required String value}) async {
+    await firebase.setUserProperty(name: name, value: value);
+  }
 }
 
 void logEvent(Event event, {Map<String, String> parameters = const {}}) {
@@ -174,7 +183,7 @@ class AnalyticsRouteObserver extends RouteObserver<PageRoute<dynamic>> {
     }
 
     try {
-      await getAnalytics().firebase.setCurrentScreen(screenName: screenName);
+      await getAnalytics().setCurrentScreen(screenName: screenName);
     } catch (e, stackTrace) {
       Log.e("AnalyticsRouteObserver", ex: e, stacktrace: stackTrace);
     }

lib/app.dart

@@ -114,15 +114,15 @@ class JournalApp extends StatefulWidget {
     JournalApp.analytics.setAnalyticsCollectionEnabled(enabled);
 
     if (enabled) {
-      getAnalytics().firebase.setUserProperty(
-            name: 'proMode',
-            value: appSettings.proMode.toString(),
-          );
+      getAnalytics().setUserProperty(
+        name: 'proMode',
+        value: appSettings.proMode.toString(),
+      );
 
-      getAnalytics().firebase.setUserProperty(
-            name: 'proExpirationDate',
-            value: appSettings.proExpirationDate.toString(),
-          );
+      getAnalytics().setUserProperty(
+        name: 'proExpirationDate',
+        value: appSettings.proExpirationDate.toString(),
+      );
     }
   }
 

lib/repository.dart

@@ -137,10 +137,10 @@ class Repository with ChangeNotifier {
     notesFolder = NotesFolderFS(null, _gitRepo.gitDirPath, settings);
 
     // Makes it easier to filter the analytics
-    getAnalytics().firebase.setUserProperty(
-          name: 'onboarded',
-          value: remoteGitRepoConfigured.toString(),
-        );
+    getAnalytics().setUserProperty(
+      name: 'onboarded',
+      value: remoteGitRepoConfigured.toString(),
+    );
 
     var cachePath = p.join(cacheDir, "cache.json");
     _notesCache = NotesCache(