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.Client/Interfaces/IClientPreferencesManager.cs

@@ -0,0 +1,13 @@
+using Content.Shared.Preferences;
+
+namespace Content.Client.Interfaces
+{
+    public interface IClientPreferencesManager
+    {
+        void Initialize();
+        GameSettings Settings { get; }
+        PlayerPreferences Preferences { get; }
+        void SelectCharacter(int slot);
+        void UpdateCharacter(ICharacterProfile profile, int slot);
+    }
+}