Re-work MaterialComponent

sky/examples/stocks-fn/stockrow.dart

 part of stocksapp;
 
-class StockRow extends Material {
+class StockRow extends Component {
 
   Stock stock;
 
   static Style _style = new Style('''
     transform: translateX(0);
     display: flex;
     align-items: center;
     border-bottom: 1px solid #F4F4F4;
     padding-top: 16px;
     padding-left: 16px;
@@ skipping 41 matching lines @@
         style: _lastSaleStyle,
         children: [new Text(lastSale)]
       ),
       new Container(
         key: 'Change',
         style: _changeStyle,
         children: [new Text(changeInPrice)]
       )
     ];
 
-    children.add(super.build());
-
-    return new Container(
+    return new Material(
       style: _style,
       children: children
     );
   }
 }