Add DosCenter deserialization test, fix issues

SabreTools.Models/DosCenter/DosCenter.cs

@@ -23,5 +23,12 @@ namespace SabreTools.Models.DosCenter
 
         /// <remarks>comment</remarks>
         public string? Comment { get; set; }
+
+        #region DO NOT USE IN PRODUCTION
+
+        /// <remarks>Should be empty</remarks>
+        public string[] ADDITIONAL_ELEMENTS { get; set; }
+
+        #endregion
     }
 }