Create a LargeTextureStore for cached (but not atlased) global textures

Also
- Fixes first transition depth being incorrect.
- Improves smoothness of transitions (and adds a slight delay to offset from screen switches).

osu.Game/Graphics/Textures/LargeTextureStore.cs

@@ -0,0 +1,18 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Framework.Graphics.Textures;
+using osu.Framework.IO.Stores;
+
+namespace osu.Game.Graphics.Textures
+{
+    /// <summary>
+    /// A texture store that bypasses atlasing.
+    /// </summary>
+    public class LargeTextureStore : TextureStore
+    {
+        public LargeTextureStore(IResourceStore<RawTexture> store = null) : base(store, false)
+        {
+        }
+    }
+}