Add basic custom data directory support

osu.Game/Configuration/StorageConfigManager.cs

@@ -0,0 +1,30 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Configuration;
+using osu.Framework.Platform;
+
+namespace osu.Game.Configuration
+{
+    public class StorageConfigManager : IniConfigManager<StorageConfig>
+    {
+        protected override string Filename => "storage.ini";
+
+        public StorageConfigManager(Storage storage)
+            : base(storage)
+        {
+        }
+
+        protected override void InitialiseDefaults()
+        {
+            base.InitialiseDefaults();
+
+            Set(StorageConfig.FullPath, string.Empty);
+        }
+    }
+
+    public enum StorageConfig
+    {
+        FullPath,
+    }
+}