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

sky/sdk/lib/example/stocks2/lib/stock_app.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/rendering/sky_binding.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/theme/theme_data.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/theme.dart';
@@ skipping 62 matching lines @@
 }
 
 void main() {
   print("starting stocks app!");
   runApp(new StocksApp());
   SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
     // SkyBinding.instance.debugDumpRenderTree();
   };
 }