Add OfflineList deserialization test, fix issues

SabreTools.Models/OfflineList/Dat.cs

@@ -6,10 +6,28 @@ namespace SabreTools.Models.OfflineList
     [XmlRoot("dat")]
     public class Dat
     {
+        [XmlAttribute(Namespace = "http://www.w3.org/2001/XMLSchema-instance", AttributeName = "noNamespaceSchemaLocation")]
+        public string? NoNamespaceSchemaLocation { get; set; }
+
         [XmlElement("configuration")]
         public Configuration? Configuration { get; set; }
 
         [XmlElement("games")]
         public Games? Games { get; set; }
+
+        [XmlElement("gui")]
+        public GUI? GUI { get; set; }
+
+        #region DO NOT USE IN PRODUCTION
+
+        /// <remarks>Should be empty</remarks>
+        [XmlAnyAttribute]
+        public XmlAttribute[]? ADDITIONAL_ATTRIBUTES { get; set; }
+
+        /// <remarks>Should be empty</remarks>
+        [XmlAnyElement]
+        public object[]? ADDITIONAL_ELEMENTS { get; set; }
+
+        #endregion
     }
 }