Add a confirmation dialog to stock app Settings page and style it by default

sky/tests/widgets/dialog.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/dialog.dart';
 
 import '../resources/display_list.dart';
 
 main() async {
   WidgetTester tester = new WidgetTester();
 
   await tester.test(() {
     return new Dialog(
       title: new Text("I am a title"),
       content: new Text("I am some content"),
-      actions: new Text("I am some actions")
+      actions: [new Text("I am some actions")]
     );
   });
 
   tester.endTest();
 }