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

sky/examples/stocks2/lib/stock_menu.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/checkbox.dart';
-import 'package:sky/widgets/popup_menu.dart';
-import 'package:sky/widgets/basic.dart';
-import 'package:sky/framework/theme/view_configuration.dart';
-
-class StockMenu extends Component {
-
-  StockMenu({
-    String key,
-    this.controller,
-    this.autorefresh: false,
-    this.onAutorefreshChanged
-  }) : super(key: key);
-
-  final PopupMenuController controller;
-  final bool autorefresh;
-  final ValueChanged onAutorefreshChanged;
-
-  Widget build() {
-    var checkbox = new Checkbox(
-      value: this.autorefresh,
-      onChanged: this.onAutorefreshChanged
-    );
-
-    return new Positioned(
-      child: new PopupMenu(
-        controller: controller,
-        items: [
-          new Text('Add stock'),
-          new Text('Remove stock'),
-          new Flex([new Flexible(child: new Text('Autorefresh')), checkbox]),
-        ],
-        level: 4
-      ),
-      right: 8.0,
-      top: 8.0 + kStatusBarHeight
-    );
-  }
-}