General uncontroversial cleanup:

- Made private methods static where possible (runtime can elide checking the object for null).
- Declared attribute classes as sealed (allows reflection on attributes to complete faster).
- Moved some static cctor's into field initializers (static cctor's are slower than static field initializers).
- Made classes static if they contained only static methods (can't create instances of useless objects).
- Use inferable Exts.Lazy and not new Lazy<T>().
- Added required STAThread attribute to CrashDialog.
- Removed unused parameters in private methods.
- Added Serializable attribute to exceptions.
- Added parameter name in calls to ArgumentNullException.
- Use of as operator instead of is + cast.
- Changed (x as Foo).Bar anti-pattern into ((Foo)x).Bar. Results in sensible cast exceptions on error rather than null dereferences.
- Removed unused method in NullShader.

OpenRA.Mods.RA/Orders/PowerDownOrderGenerator.cs

@@ -31,10 +31,10 @@ namespace OpenRA.Mods.RA.Orders
 			if (mi.Button == MouseButton.Right)
 				world.CancelInputMode();
 
-			return OrderInner(world, xy, mi);
+			return OrderInner(world, mi);
 		}
 
-		IEnumerable<Order> OrderInner(World world, CPos xy, MouseInput mi)
+		IEnumerable<Order> OrderInner(World world, MouseInput mi)
 		{
 			if (mi.Button == MouseButton.Left)
 			{
@@ -59,7 +59,7 @@ namespace OpenRA.Mods.RA.Orders
 		public string GetCursor(World world, CPos xy, MouseInput mi)
 		{
 			mi.Button = MouseButton.Left;
-			return cursor + (OrderInner(world, xy, mi).Any()	? "" : "-blocked");
+			return cursor + (OrderInner(world, mi).Any()	? "" : "-blocked");
 		}
 	}