Adds add2app Flutter module and an iOS project to run it. (#126)

experimental/add_to_app/example_module/test/widget_test.dart

@@ -0,0 +1,12 @@
+// This is a basic Flutter widget test.
+//
+// To perform an interaction with a widget in your test, use the WidgetTester
+// utility that Flutter provides. For example, you can send tap and scroll
+// gestures. You can also use WidgetTester to find child widgets in the widget
+// tree, read text, and verify that the values of widget properties are correct.
+
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('This test always passes', (tester) async {});
+}