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.Cnc/ProductionAirdrop.cs

@@ -48,7 +48,8 @@ namespace OpenRA.Mods.Cnc
 			foreach (var tower in self.TraitsImplementing<INotifyDelivery>())
 				tower.IncomingDelivery(self);
 
-			var actorType = (Info as ProductionAirdropInfo).ActorType;
+			var info = (ProductionAirdropInfo)Info;
+			var actorType = info.ActorType;
 
 			owner.World.AddFrameEndTask(w =>
 			{
@@ -70,7 +71,7 @@ namespace OpenRA.Mods.Cnc
 					foreach (var cargo in self.TraitsImplementing<INotifyDelivery>())
 						cargo.Delivered(self);
 					self.World.AddFrameEndTask(ww => DoProduction(self, producee, exit));
-					Sound.PlayNotification(self.World.Map.Rules, self.Owner, "Speech", (Info as ProductionAirdropInfo).ReadyAudio, self.Owner.Country.Race);
+					Sound.PlayNotification(self.World.Map.Rules, self.Owner, "Speech", info.ReadyAudio, self.Owner.Country.Race);
 				}));
 
 				a.QueueActivity(new Fly(a, Target.FromCell(endPos)));