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

Implement Serialization framework from v5 U4-968

src/Umbraco.Core/Serialization/ServiceStackXmlSerializer.cs

@@ -0,0 +1,26 @@
+using System;
+using System.IO;
+using System.Text;
+using ServiceStack.Text;
+
+namespace Umbraco.Core.Serialization
+{
+    public class ServiceStackXmlSerializer : ISerializer
+    {
+        public ServiceStackXmlSerializer()
+        {
+        }
+
+        public object FromStream(Stream input, Type outputType)
+        {
+            return XmlSerializer.DeserializeFromStream(outputType, input);
+        }
+
+        public IStreamedResult ToStream(object input)
+        {
+            string output = XmlSerializer.SerializeToString(input);
+            var stream = new MemoryStream(Encoding.UTF8.GetBytes(output));
+            return new StreamedResult(stream, true);
+        }
+    }
+}