Add a new Theme widget to control color and text color of apps

sky/examples/widgets/styled_text.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/painting/text_style.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/theme/colors.dart';
+import 'package:sky/theme/theme_data.dart';
 import 'package:sky/theme/typography.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/material.dart';
 import 'package:sky/widgets/scaffold.dart';
+import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/tool_bar.dart';
 import 'package:sky/widgets/widget.dart';
 
 
 class StyledTextApp extends App {
 
   StyledTextApp() {
     toText = toStyledText;
     nameLines = dialogText
       .split('\n')
@@ skipping 74 matching lines @@
           justifyContent: FlexJustifyContent.center,
           alignItems: FlexAlignItems.flexStart
         )
       );
 
     Listener interactiveBody = new Listener(
       child: body,
       onPointerDown: toggleToTextFunction
     );
 
-    return new Scaffold(
-      body: new Material(child: interactiveBody),
-      toolbar: new ToolBar(
-        center: new Text('Hal and Dave', style: white.title),
-        backgroundColor: Blue[500]
+    return new Theme(
+      data: new ThemeData(color: Blue, text: white),
+      child: new Scaffold(
+        body: new Material(child: interactiveBody),
+        toolbar: new ToolBar(
+          center: new Text('Hal and Dave', style: white.title)
+        )
       )
     );
   }
 }
 
 void main() {
   runApp(new StyledTextApp());
   SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
     // SkyBinding.instance.debugDumpRenderTree();
   };
 }