Added preferences backend (#465)

* Added preferences backend

* Gender -> Sex

* ClientPreferencesManager properties

* Username validation

* Fixed client init

* WIP db

* Actually working sqlite db

* Dropped shitty sqlite libraries, dropped DbUp, added MigrationManager

* Added profile deletion, test

* Docs, sanity, tests, cleanup

* Cleaned up profile and appearance, fixed running on .net core

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>

Content.Shared/Preferences/GameSettings.cs

@@ -0,0 +1,20 @@
+using System;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Preferences
+{
+    /// <summary>
+    /// Information needed for character setup.
+    /// </summary>
+    [Serializable, NetSerializable]
+    public class GameSettings
+    {
+        private int _maxCharacterSlots;
+
+        public int MaxCharacterSlots
+        {
+            get => _maxCharacterSlots;
+            set => _maxCharacterSlots = value;
+        }
+    }
+}