updated: navigation_drawer example with code refactoring

navigation_drawer/lib/screens/settings.dart

@@ -0,0 +1,18 @@
+import 'package:flutter/material.dart';
+
+class SettingsScreen extends StatelessWidget {
+  static String routeName = "/settings";
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      appBar: new AppBar(
+        title: new Text("Settings"),
+      ),
+      body: new Container(
+          child: new Center(
+        child: new Text("Settings Screen"),
+      )),
+    );
+  }
+}