[101] Restore legacy to data.dart and product.dart (#75)

Author: tianlunlee

mdc_100_series/lib/model/data.dart

@@ -15,7 +15,7 @@
 import 'product.dart';
 
 List<Product> getProducts(Category category) {
-  allProducts = <Product>[
+  const allProducts = <Product>[
     Product(
       category: Category.accessories,
       id: 0,

mdc_100_series/lib/model/product.dart

@@ -17,7 +17,7 @@ import 'package:flutter/foundation.dart';
 enum Category { all, accessories, clothing, home, }
 
 class Product {
-  Product({
+  const Product({
     @required this.category,
     @required this.id,
     @required this.isFeatured,