Refactor weather to use Z traits, assorted related cleanup (#34633)

* Add a proc for getting the station center

* Add a couple of comments to ZTRAIT defines

* Remove unused global_map list

* Refactor weather to use the trait system

* Un-hardcode the transit z-level

* Use Z traits to determine Portal Storm event areas

* Fix loading away missions containing anything that reads traits

code/modules/mapping/map_template.dm

@@ -52,7 +52,8 @@
 	var/x = round((world.maxx - width)/2)
 	var/y = round((world.maxy - height)/2)
 
-	var/list/bounds = maploader.load_map(file(mappath), x, y)
+	var/datum/space_level/level = SSmapping.add_new_zlevel(name, UNAFFECTED, list(ZTRAIT_AWAY = TRUE))
+	var/list/bounds = maploader.load_map(file(mappath), x, y, level.z_value, no_changeturf=(SSatoms.initialized == INITIALIZATION_INSSATOMS))
 	if(!bounds)
 		return FALSE