Clamp, scroll, scrollspeed, sliders

Reduced clamp duplication
Fixed scrolling speed issue
Modified scrollspeed slider to use a range
Fixed scrollspeed, volume, and sound sliders not showing current setting.

OpenRA.Game/Exts.cs

@@ -67,15 +67,5 @@ namespace OpenRA
 					Log.Write("perf", text, x, dt * 1000, Game.LocalTick);
 			});
 		}
-
-		public static T Clamp<T>(this T val, T min, T max) where T : IComparable<T>
-		{
-			if (val.CompareTo(min) < 0)
-				return min;
-			else if (val.CompareTo(max) > 0)
-				return max;
-			else
-				return val;
-		}
 	}
 }