Added identifier and fetch time product listings; Added persistence to AdafruitShop.

Implemented in AdafruitShop.

AdafruitShop Product listing data now persisted.

AdafruitShop configuration now persisted.

Props-Modules/Props.Shop/Adafruit/Persistence/Configuration.cs

@@ -0,0 +1,19 @@
+namespace Props.Shop.Adafruit.Persistence
+{
+    public class Configuration
+    {
+        public const string FILE_NAME = "config.json";
+        public int MinDownloadInterval { get; set; }
+        public int CacheLifespan { get; set; }
+        public float Similarity { get; set; }
+        public string ProductListingCacheFileName { get; set; }
+
+        public Configuration()
+        {
+            MinDownloadInterval = 5 * 60 * 1000;
+            Similarity = 0.8f;
+            CacheLifespan = 5 * 60 * 1000;
+            ProductListingCacheFileName = "ProductListings.json";
+        }
+    }
+}

Props-Modules/Props.Shop/Adafruit/Persistence/ProductListingCacheData.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using Props.Shop.Framework;
+
+namespace Props.Shop.Adafruit.Persistence
+{
+    public class ProductListingCacheData
+    {
+        public const string FILE_NAME = "Product-listing-cache.json";
+        public DateTime LastUpdatedUtc { get; private set; }
+        public IReadOnlyDictionary<string, IList<ProductListing>> ProductListings { get; set; }
+
+        public ProductListingCacheData(IReadOnlyDictionary<string, IList<ProductListing>> productListings)
+        {
+            this.ProductListings = productListings;
+            LastUpdatedUtc = DateTime.UtcNow;
+        }
+
+        public ProductListingCacheData()
+        {
+        }
+    }
+}