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

sky/examples/hello_world/hello_world.dart

Index: sky/examples/hello_world/hello_world.dart
diff --git a/sky/examples/hello_world/hello_world.dart b/sky/examples/hello_world/hello_world.dart
deleted file mode 100644
index e20978844d10f8c7caede32ccd867f74adece800..0000000000000000000000000000000000000000
--- a/sky/examples/hello_world/hello_world.dart
+++ /dev/null
@@ -1,11 +0,0 @@
-// 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/framework/fn.dart';
-
-class HelloWorldApp extends App {
-  UINode build() {
-    return new Text('Hello, world!');
-  }
-}