Move sky/examples to sky/sdk/lib/example, and code changes to support that change. Fixes T277.

sky/sdk/lib/example/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';
@@ skipping 107 matching lines @@
   }
 }
 
 void main() {
   runApp(new StyledTextApp());
   SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
     // SkyBinding.instance.debugDumpRenderTree();
   };
 }