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/Render/RenderBuildingWall.cs

@@ -77,7 +77,7 @@ namespace OpenRA.Mods.RA.Render
 			dirty = false;
 		}
 
-		void UpdateNeighbours(Actor self)
+		static void UpdateNeighbours(Actor self)
 		{
 			var vec = new CVec(1, 1);
 			var neighbours = self.World.FindActorsInBox(self.Location - vec, self.Location + vec)