Updates base entities to contain a DeletedDate if the entity gets deleted

src/Umbraco.Core/Models/EntityBase/Entity.cs

@@ -101,6 +101,9 @@ namespace Umbraco.Core.Models.EntityBase
             set { SetPropertyValueAndDetectChanges(value, ref _updateDate, Ps.Value.UpdateDateSelector); }           
         }
 
+        [IgnoreDataMember]
+        public DateTime? DeletedDate { get; set; }
+
         internal virtual void ResetIdentity()
         {
             _hasIdentity = false;

src/Umbraco.Core/Models/EntityBase/IAggregateRoot.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Marker interface for aggregate roots
     /// </summary>
-    public interface IAggregateRoot : IEntity
+    public interface IAggregateRoot : IEntityDeleted
     {
          
     }

src/Umbraco.Core/Models/EntityBase/IEntity.cs

@@ -3,6 +3,12 @@ using System.Runtime.Serialization;
 
 namespace Umbraco.Core.Models.EntityBase
 {
+    public interface IEntityDeleted : IEntity
+    {
+        [DataMember]
+        DateTime? DeletedDate { get; set; }
+    }
+
     /// <summary>
     /// Defines an Entity.
     /// Entities should always have an Id, Created and Modified date