Added spawn origin flags.

- Added new spawn flags that allow for checking if an actor was spawned by the level, the console, or ACS/DECORATE/ZScript.

src/playsim/p_mobj.cpp

@@ -5352,6 +5352,7 @@ void AActor::LevelSpawned ()
 	{
 		flags &= ~MF_DROPPED;
 	}
+	SpawnFlags |= MTF_MAPTHING;
 	HandleSpawnFlags ();
 }