Support for background images on cards, style demo home

sky/sdk/example/stocks/lib/main.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/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';
 import 'package:sky/widgets/widget.dart';
 
 import 'stock_data.dart';
 import 'stock_home.dart';
 import 'stock_settings.dart';
 import 'stock_types.dart';
 
@@ skipping 62 matching lines @@
     return new Theme(
       data: theme,
         child: new Navigator(_navigationState)
      );
    }
 }
 
 void main() {
   runApp(new StocksApp());
 }