Implement App Icon selection

- added 2 additional app icons to choose from
- added translation string for settings screen
- smaller changes + formatting some touched files

lib/utils/app_icon_changer.dart

@@ -0,0 +1,25 @@
+import 'package:flutter/services.dart';
+import 'package:logging/logging.dart';
+
+class AppIconChanger {
+  static const MethodChannel _channel = MethodChannel('change_icon');
+
+  static Future<void> changeIcon(LauncherIcon icon) async {
+    try {
+      await _channel.invokeMethod('changeIcon', {'iconName': icon.key});
+    } on PlatformException catch (e) {
+      Logger.root.severe('Failed to change icon: ${e.message}');
+    }
+  }
+
+  static List<LauncherIcon> get availableIcons => LauncherIcon.values;
+}
+
+enum LauncherIcon {
+  defaultIcon('DefaultIcon'),
+  catIcon('CatIcon'),
+  deezerIcon('DeezerBlueIcon');
+
+  final String key;
+  const LauncherIcon(this.key);
+}