Split layout2.dart into several files

sky/examples/stocks2/lib/stock_row.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/framework/components2/ink_well.dart';
 import 'package:sky/framework/fn2.dart';
-import 'package:sky/framework/layout2.dart';
 import 'package:sky/framework/theme/typography.dart' as typography;
 import 'stock_arrow.dart';
 import 'stock_data.dart';
 
 class StockRow extends Component {
   static final Style _style = new Style('''
     align-items: center;
     border-bottom: 1px solid #F4F4F4;
     padding-top: 16px;
     padding-left: 16px;
@@ skipping 45 matching lines @@
       new Container(
         key: 'Change',
         style: _changeStyle,
         children: [new Text(changeInPrice)]
       )
     ];
 
     return new StyleNode(new InkWell(children: children), _style);
   }
 }