Add IconUrl property to MessageApplication

src/Discord.Net.Core/Entities/Messages/MessageApplication.cs

@@ -26,6 +26,13 @@ namespace Discord
         ///     Gets the ID of the application's icon.
         /// </summary>
         public string Icon { get; set; }
+
+        /// <summary>
+        ///     Gets the Url of the application's icon.
+        /// </summary>
+        public string IconUrl
+            => $"https://cdn.discordapp.com/app-icons/{Id}/{Icon}";
+
         /// <summary>
         ///     Gets the name of the application.
         /// </summary>