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/ServerTraits/LobbyCommands.cs

@@ -54,7 +54,7 @@ namespace OpenRA.Mods.RA.Server
 			return true;
 		}
 
-		void CheckAutoStart(S server, Connection conn, Session.Client client)
+		static void CheckAutoStart(S server)
 		{
 			var playerClients = server.LobbyInfo.Clients.Where(c => c.Bot == null && c.Slot != null);
 
@@ -93,7 +93,7 @@ namespace OpenRA.Mods.RA.Server
 
 						server.SyncLobbyClients();
 
-						CheckAutoStart(server, conn, client);
+						CheckAutoStart(server);
 
 						return true;
 					}},
@@ -131,7 +131,7 @@ namespace OpenRA.Mods.RA.Server
 						client.Slot = s;
 						S.SyncClientToPlayerReference(client, server.Map.Players[s]);
 						server.SyncLobbyClients();
-						CheckAutoStart(server, conn, client);
+						CheckAutoStart(server);
 
 						return true;
 					}},