Added first draft of login and tour select page

lib/model/supplier.dart

@@ -0,0 +1,18 @@
+import 'package:app_gaslieferung/model/address.dart';
+
+import 'car.dart';
+
+class Supplier {
+  String id;
+  String name;
+  Address address;
+  String? phoneNumber;
+  List<Car> cars;
+
+  Supplier({
+    required this.id,
+    required this.name,
+    required this.cars,
+    required this.address,
+  });
+}