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/IrcLogic.cs

@@ -152,7 +152,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 			};
 		}
 
-		string ChooseNickname(string nickname)
+		static string ChooseNickname(string nickname)
 		{
 			if (!IrcUtils.IsNickname(nickname))
 			{
@@ -172,7 +172,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 			IrcClient.Instance.Connect(s.Hostname, s.Port, s.ConnectionTimeout, nickname, s.Username ?? nickname, s.Realname ?? nickname);
 		}
 
-		Widget MakeLabelWidget(LabelWidget template, object item)
+		static Widget MakeLabelWidget(LabelWidget template, object item)
 		{
 			var itemString = item.ToString();
 			var widget = (LabelWidget)template.Clone();