add timestamp

Application/Helpers/SessionFiles.cs

@@ -131,7 +131,8 @@ namespace CodeEditorApi.Helpers
             var session = new Session
             {
                 Id = Guid.Parse(strId),
-                NumberOfChanges = files.Length
+                NumberOfChanges = files.Length,
+                Timestamp = Directory.GetCreationTime(path)
             };
 
             return session;

Application/Session.cs

@@ -4,5 +4,6 @@
     {
         public Guid Id { get; set; }
         public int NumberOfChanges { get; set; }
+        public DateTime Timestamp { get; set; }
     }
 }