Move sky-*.sky into framework/elements

sky/examples/scrolling/scrolling.sky

 <!--
 // 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 src="/sky/framework/sky-element.sky" />
-<import src="/sky/framework/sky-scrollable.sky" />
+<import src="/sky/framework/elements/sky-element.sky" />
+<import src="/sky/framework/elements/sky-scrollable.sky" />
 
 <sky-element>
 <template>
   <style>
   sky-scrollable {
     margin: 20px;
     height: 400px;
     border: 2px solid blue;
   }
   </style>
@@ skipping 11 matching lines @@
       Element div = document.createElement('div');
       div.setChild(new Text(city['name']));
       parent.appendChild(div);
     }
   }
 }
 
 _init(script) => register(script, Scrolling);
 </script>
 </sky-element>