Introduce the concept of SkinComponents

Removes reliance on string lookups and better defines elements for introduction into database

osu.Game.Rulesets.Catch/CatchSkinComponents.cs

@@ -0,0 +1,10 @@
+// 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.
+
+namespace osu.Game.Rulesets.Catch
+{
+    public enum CatchSkinComponents
+    {
+        Catcher
+    }
+}