Enabling nuget package restore and removing referenced nupkg files from repo U4-997

Implement Serialization framework from v5 U4-968

src/Umbraco.Core/Serialization/AbstractSerializationService.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Umbraco.Core.Serialization
+{
+    public abstract class AbstractSerializationService
+    {
+        /// <summary>
+        ///   A sequence of <see cref="IFormatter" /> registered with this serialization service.
+        /// </summary>
+        public IEnumerable<IFormatter> Formatters { get; set; }
+
+        /// <summary>
+        ///   Finds an <see cref="IFormatter" /> with a matching <paramref name="intent" /> , and deserializes the <see cref="Stream" /> <paramref
+        ///    name="input" /> to an object graph.
+        /// </summary>
+        /// <param name="input"> </param>
+        /// <param name="outputType"> </param>
+        /// <param name="intent"> </param>
+        /// <returns> </returns>
+        public abstract object FromStream(Stream input, Type outputType, string intent = null);
+
+        /// <summary>
+        ///   Finds an <see cref="IFormatter" /> with a matching <paramref name="intent" /> , and serializes the <paramref
+        ///    name="input" /> object graph to an <see cref="IStreamedResult" /> .
+        /// </summary>
+        /// <param name="input"> </param>
+        /// <param name="intent"> </param>
+        /// <returns> </returns>
+        public abstract IStreamedResult ToStream(object input, string intent = null);
+    }
+}