Delete drawerController and make drawer handle back behavior natively

sky/sdk/example/fitness/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/widgets/basic.dart';
 import 'package:sky/widgets/navigator.dart';
 import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/widget.dart';
 
 import 'measurement.dart';
 import 'home.dart';
 import 'settings.dart';
 import 'fitness_types.dart';
 
 class FitnessApp extends App {
 
   NavigationState _navigationState;
-  FitnessApp();
 
   void initState() {
     _navigationState = new NavigationState([
       new Route(
         name: '/', 
         builder: (navigator, route) => new HomeFragment(navigator, _userData)
       ),
       new Route(
         name: '/settings',
         builder: (navigator, route) => new SettingsFragment(navigator, backupSetting, settingsUpdater)
@@ skipping 33 matching lines @@
         accentColor: colors.PinkAccent[200]
       ),
       child: new Navigator(_navigationState)
     );
   }
 }
 
 void main() {
   runApp(new FitnessApp());
 }