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/PlayerPreferences.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Robust.Shared.Interfaces.Serialization;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Preferences
+{
+    /// <summary>
+    /// Contains all player characters and the index of the currently selected character.
+    /// Serialized both over the network and to disk.
+    /// </summary>
+    [Serializable, NetSerializable]
+    public class PlayerPreferences
+    {
+        public static PlayerPreferences Default()
+        {
+            return new PlayerPreferences
+            {
+                Characters = new List<ICharacterProfile>
+                {
+                    HumanoidCharacterProfile.Default()
+                },
+                SelectedCharacterIndex = 0
+            };
+        }
+
+        private List<ICharacterProfile> _characters;
+        private int _selectedCharacterIndex;
+
+        /// <summary>
+        /// All player characters.
+        /// </summary>
+        public List<ICharacterProfile> Characters
+        {
+            get => _characters;
+            set => _characters = value;
+        }
+
+        /// <summary>
+        /// Index of the currently selected character.
+        /// </summary>
+        public int SelectedCharacterIndex
+        {
+            get => _selectedCharacterIndex;
+            set => _selectedCharacterIndex = value;
+        }
+
+        /// <summary>
+        /// Retrieves the currently selected character.
+        /// </summary>
+        public ICharacterProfile SelectedCharacter => Characters.ElementAtOrDefault(SelectedCharacterIndex);
+    }
+}