Add persistence to settings service

lib/main.dart

@@ -39,7 +39,11 @@ void main() async {
   final entryManagerService = EntryManagerService();
   final timelineManager = TimelineManager();
   final galleryService = GalleryService();
-  getIt.registerLazySingleton(() => SettingsService());
+  getIt.registerSingletonAsync(() async {
+    final service = SettingsService();
+    await service.initialize();
+    return service;
+  });
   getIt.registerLazySingleton<ConnectionsManager>(() => ConnectionsManager());
   getIt.registerLazySingleton<HashtagService>(() => HashtagService());
   getIt.registerSingleton(galleryService);

lib/services/setting_service.dart

@@ -1,12 +1,30 @@
 import 'package:flutter/foundation.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 
 class SettingsService extends ChangeNotifier {
-  var _lowBandwidthMode = true;
+  late final SharedPreferences _prefs;
+  var _initialized = false;
+
+  SettingsService();
+
+  var _lowBandwidthMode = false;
 
   bool get lowBandwidthMode => _lowBandwidthMode;
 
   set lowBandwidthMode(bool value) {
     _lowBandwidthMode = value;
+    _prefs.setBool(_lowBandwidthModeKey, _lowBandwidthMode);
     notifyListeners();
   }
+
+  Future<void> initialize() async {
+    if (_initialized) {
+      return;
+    }
+    _prefs = await SharedPreferences.getInstance();
+    _lowBandwidthMode = _prefs.getBool(_lowBandwidthModeKey) ?? false;
+    _initialized = true;
+  }
 }
+
+const _lowBandwidthModeKey = 'LowBandwidthMode';