Rename App to MaterialApp

MaterialApp assumes that you're using material design.

Also move radial reaction and fix imports for stats box.
diff --git a/examples/stocks/lib/main.dart b/examples/stocks/lib/main.dart
index 1a46790..f791c55 100644
--- a/examples/stocks/lib/main.dart
+++ b/examples/stocks/lib/main.dart
@@ -87,7 +87,7 @@
   }
 
   Widget build(BuildContext context) {
-    return new App(
+    return new MaterialApp(
       title: 'Stocks',
       theme: theme,
       routes: <String, RouteBuilder>{