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.Renderer.Null/NullGraphicsDevice.cs

@@ -71,7 +71,6 @@ namespace OpenRA.Renderer.Null
 		public void SetVec(string name, float[] vec, int length) { }
 		public void SetTexture(string param, ITexture texture) { }
 		public void SetMatrix(string param, float[] mtx) { }
-		public void Commit() { }
 		public void Render(Action a) { }
 	}