Implemented basic structure

lib/data/dto/game.dart

@@ -0,0 +1,6 @@
+class Game {
+  final String id;
+  final String name;
+
+  Game({required this.id, required this.name});
+}

lib/data/dto/group.dart

@@ -0,0 +1,9 @@
+import 'package:game_tracker/data/methods/dto/player.dart';
+
+class Group {
+  final String id;
+  final String name;
+  final List<Player> members;
+
+  Group({required this.id, required this.name, required this.members});
+}

lib/data/dto/player.dart

@@ -0,0 +1,6 @@
+class Player {
+  final String id;
+  final String username;
+
+  Player({required this.id, required this.username});
+}