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/Widgets/Logic/MainMenuLogic.cs

@@ -180,7 +180,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 			}
 		}
 
-		string GetNewsCacheFile()
+		static string GetNewsCacheFile()
 		{
 			var cacheDir = Path.Combine(Platform.SupportDir, "cache", Game.modData.Manifest.Mod.Id);
 			Directory.CreateDirectory(cacheDir);
@@ -201,7 +201,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 			public string Content;
 		}
 
-		IEnumerable<NewsItem> ReadNews(byte[] bytes)
+		static IEnumerable<NewsItem> ReadNews(byte[] bytes)
 		{
 			var str = Encoding.UTF8.GetString(bytes);
 			return MiniYaml.FromString(str).Select(node => new NewsItem