Make many internal classes and methods public

This is important when using dynamic compiling to rapidly iterate. Until we actually split projects out into pieces (like the abstract ruleset project we have talked about) there is no advantage to using internal in the osu! game code.

osu.Game/Graphics/UserInterface/Volume/VolumeControl.cs

@@ -11,7 +11,7 @@ using osu.Game.Input.Bindings;
 
 namespace osu.Game.Graphics.UserInterface.Volume
 {
-    internal class VolumeControl : OverlayContainer
+    public class VolumeControl : OverlayContainer
     {
         private readonly VolumeMeter volumeMeterMaster;
 
@@ -119,4 +119,4 @@ namespace osu.Game.Graphics.UserInterface.Volume
             this.Delay(1000).Schedule(Hide, out popOutDelegate);
         }
     }
-}
+}