Start creating Dictionary-based internal models

SabreTools.Models/Internal/Release.cs

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+using System.Xml.Serialization;
+using Newtonsoft.Json;
+
+namespace SabreTools.Models.Internal
+{
+    [JsonObject("release"), XmlRoot("release")]
+    public class Release : DatItem
+    {
+        #region Keys
+
+        /// <remarks>string</remarks>
+        public const string DateKey = "date";
+
+        /// <remarks>(yes|no) "no"</remarks>
+        public const string DefaultKey = "default";
+
+        /// <remarks>string</remarks>
+        public const string LanguageKey = "language";
+
+        /// <remarks>string</remarks>
+        public const string NameKey = "name";
+
+        /// <remarks>string</remarks>
+        public const string RegionKey = "region";
+
+        #endregion
+
+        public Release() => Type = ItemType.Release;
+    }
+}