fix(core): Updates expansion and map configurations (fixes map issues) (#570)

- [X] Adds question about expansion at start of server
- [X] Adds question about client version to determine old have and map diffs
- [X] Adds config setting "maps.enablePre6000Trammel"
- [X] Rearranges some of the loading order.
- [X] Added support for deserializing nullable enums from json

TODO:
Expand the nullable enums deserialization factory to work with any type by pulling the factory and creating an instance of the converter.

Projects/Server/Configuration/ServerSettings.cs

@@ -0,0 +1,36 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2021 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: ServerSettings.cs                                               *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Collections.Generic;
+using System.Net;
+using System.Text.Json.Serialization;
+
+namespace Server
+{
+    public class ServerSettings
+    {
+        [JsonPropertyName("dataDirectories")]
+        public List<string> DataDirectories { get; set; } = new();
+
+        [JsonPropertyName("listeners")]
+        public List<IPEndPoint> Listeners { get; set; } = new();
+
+        [JsonPropertyName("expansion")]
+        public Expansion? Expansion { get; set; }
+
+        [JsonPropertyName("settings")]
+        public SortedDictionary<string, string> Settings { get; set; } = new();
+    }
+}