Make const folder with all necessary constants

Francesco.Recipes.World/Constants/ContentType.cs

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+namespace Francesco.Recipes.World.Constants
+{
+    public class ContentType
+    {
+        public const string Image = "image/";
+    }
+}

Francesco.Recipes.World/Constants/SortOrders.cs

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+namespace Francesco.Recipes.World.Constants
+{
+    public class SortOrders
+    {
+        public const string Newest = "newest";
+        public const string Oldest = "oldest";
+    }
+}