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/Activities/LayMines.cs

@@ -65,13 +65,13 @@ namespace OpenRA.Mods.RA.Activities
 			return new Wait(20);	// nothing to do here
 		}
 
-		bool ShouldLayMine(Actor self, CPos p)
+		static bool ShouldLayMine(Actor self, CPos p)
 		{
 			// if there is no unit (other than me) here, we want to place a mine here
 			return !self.World.ActorMap.GetUnitsAt(p).Any(a => a != self);
 		}
 
-		void LayMine(Actor self)
+		static void LayMine(Actor self)
 		{
 			var limitedAmmo = self.TraitOrDefault<LimitedAmmo>();
 			if (limitedAmmo != null)