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/Crates/RevealMapCrateAction.cs

@@ -25,7 +25,7 @@ namespace OpenRA.Mods.RA
 
 		bool ShouldReveal(Player collectingPlayer)
 		{
-			if ((info as RevealMapCrateActionInfo).IncludeAllies)
+			if (((RevealMapCrateActionInfo)info).IncludeAllies)
 				return collectingPlayer.World.LocalPlayer != null &&
 					collectingPlayer.Stances[collectingPlayer.World.LocalPlayer] == Stance.Ally;