Merge pull request #5864 from Garpo001/patch-1

Serialization error is thrown when creating layout or page in the dashboard when using Layouts in a Web Farm.

src/Orchard.Web/Modules/Orchard.Layouts/Models/ElementSessionState.cs

@@ -1,9 +1,12 @@
+using System;
+
 namespace Orchard.Layouts.Models {
-    public class ElementSessionState {
+        [Serializable]
+        public class ElementSessionState {
         public string TypeName { get; set; }
         public string ElementData { get; set; }
         public string ElementEditorData { get; set; }
         public int? ContentId { get; set; }
         public string ContentType { get; set; }
     }
-}
+}