Rationalize Dart mojo and sky package structure

sky/framework/components/material.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 '../fn.dart';
-import '../theme/shadows.dart';
-
-class Material extends Component {
-  static final List<Style> _shadowStyle = [
-    null,
-    new Style('box-shadow: ${Shadow[1]}'),
-    new Style('box-shadow: ${Shadow[2]}'),
-    new Style('box-shadow: ${Shadow[3]}'),
-    new Style('box-shadow: ${Shadow[4]}'),
-    new Style('box-shadow: ${Shadow[5]}'),
-  ];
-
-  UINode content;
-  int level;
-
-  Material({ Object key, this.content, this.level: 0 }) : super(key: key);
-
-  UINode build() {
-    return new StyleNode(content, _shadowStyle[level]);
-  }
-}