Move initialization and access to a singleton

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/main.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_soloud/flutter_soloud.dart';
 import 'package:wolf_dart/game_select_screen.dart';
+import 'package:wolf_dart/wolf_3d.dart';
 
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
@@ -11,6 +12,8 @@ void main() async {
     channels: Channels.stereo,
   );
 
+  await Wolf3d.I.init();
+
   runApp(
     const MaterialApp(
       home: GameSelectScreen(),