Move periodic Screen update to App level.

lib/app.dart

@@ -1,4 +1,6 @@
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:marianum_mobile/screen/pages/timetable/timetable.dart';
 import 'package:provider/provider.dart';
@@ -19,6 +21,14 @@ class App extends StatefulWidget {
 class _AppState extends State<App> {
   int currentPage = 0;
 
+  @override
+  void initState() {
+    Timer.periodic(const Duration(seconds: 30), (Timer t) => {
+      setState((){}),
+    });
+    super.initState();
+  }
+
   @override
   Widget build(BuildContext context) {
     final PageController pageController = PageController();