implemented simple material app

updated gitignore to ignore all files under build folder

simple_material_app/lib/main.dart

@@ -0,0 +1,16 @@
+import 'package:flutter/material.dart';
+
+void main() {
+  runApp(new MaterialApp(
+      title: "Simple Material App",
+      home: new Scaffold(
+        appBar: new AppBar(
+          title: new Text("Simple Material App"),
+        ),
+        body: new Container(
+          child: new Center(
+            child: new Text("Hello World!"),
+          ),
+        ),
+      )));
+}