Add provider_shopper (#87)

This is the code for the sample at https://flutter.dev/docs/development/data-and-backend/state-mgmt/simple.

provider_shopper/lib/common/theme.dart

@@ -0,0 +1,17 @@
+// Copyright 2019 The Flutter team. 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:flutter/material.dart';
+
+final appTheme = ThemeData(
+  primarySwatch: Colors.yellow,
+  textTheme: TextTheme(
+    display4: TextStyle(
+      fontFamily: 'Corben',
+      fontWeight: FontWeight.w700,
+      fontSize: 24,
+      color: Colors.black,
+    ),
+  ),
+);