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/ServerBrowserLogic.cs

@@ -289,7 +289,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 			ConnectionLogic.Connect(host, port, "", OpenLobby, DoNothing);
 		}
 
-		string GetPlayersLabel(GameServer game)
+		static string GetPlayersLabel(GameServer game)
 		{
 			if (game == null || game.Players == 0)
 				return "";
@@ -298,7 +298,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 			return "{0} / {1}".F(game.Players, map.PlayerCount == 0 ? "?" : map.PlayerCount.ToString());
 		}
 
-		string GetStateLabel(GameServer game)
+		static string GetStateLabel(GameServer game)
 		{
 			if (game == null)
 				return "";