Start creating Dictionary-based internal models

SabreTools.Models/Internal/Slot.cs

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+using System.Xml.Serialization;
+using Newtonsoft.Json;
+
+namespace SabreTools.Models.Internal
+{
+    [JsonObject("slot"), XmlRoot("slot")]
+    public class Slot : DatItem
+    {
+        #region Keys
+
+        /// <remarks>string</remarks>
+        public const string NameKey = "name";
+
+        /// <remarks>SlotOption[]</remarks>
+        public const string SlotOptionKey = "slotoption";
+
+        #endregion
+
+        public Slot() => Type = ItemType.Slot;
+    }
+}