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/awaymissions/zlevel.dm

@@ -8,7 +8,7 @@ GLOBAL_LIST_INIT(potentialRandomZlevels, generateMapList(filename = "config/away
 	if(GLOB.potentialRandomZlevels && GLOB.potentialRandomZlevels.len)
 		to_chat(world, "<span class='boldannounce'>Loading away mission...</span>")
 		var/map = pick(GLOB.potentialRandomZlevels)
-		load_new_z_level(map)
+		load_new_z_level(map, "Away Mission")
 		to_chat(world, "<span class='boldannounce'>Away mission loaded.</span>")
 
 /proc/reset_gateway_spawns(reset = FALSE)