Add mess alternative ListXML model

SabreTools.Models/Listxml/Mess.cs

@@ -0,0 +1,16 @@
+using System.Xml;
+using System.Xml.Serialization;
+
+namespace SabreTools.Models.Listxml
+{
+    [XmlRoot("mess")]
+    public class Mess
+    {
+        [XmlAttribute("version")]
+        public string? Version { get; set; }
+
+        [XmlElement("machine", typeof(Machine))]
+        [XmlElement("game", typeof(Game))]
+        public GameBase[]? Game { get; set; }
+    }
+}