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/admin/secrets.dm

@@ -422,7 +422,7 @@
 				L.fix()
 
 		if("floorlava")
-			SSweather.run_weather("the floor is lava")
+			SSweather.run_weather(/datum/weather/floor_is_lava)
 
 		if("virus")
 			if(!check_rights(R_FUN))