Wire up enum-backed dropdowns

osu.Game/Configuration/ScreenshotFormat.cs

@@ -0,0 +1,12 @@
+using System;
+namespace osu.Game.Configuration
+{
+    public enum ScreenshotFormat
+    {
+        Bmp = 0, // TODO: Figure out the best way to hide this from the dropdown
+        [DisplayName("JPG (web-friendly)")]
+        Jpg = 1,
+        [DisplayName("PNG (lossless)")]
+        Png = 2
+    }
+}