Replace hardcoded z-level numbers with a trait system

code/controllers/subsystem/minimap.dm

@@ -5,9 +5,10 @@ SUBSYSTEM_DEF(minimap)
 	var/const/MINIMAP_SIZE = 2048
 	var/const/TILE_SIZE = 8
 
-	var/list/z_levels = list(ZLEVEL_STATION_PRIMARY)
+	var/list/z_levels
 
 /datum/controller/subsystem/minimap/Initialize(timeofday)
+	z_levels = SSmapping.levels_by_trait(ZTRAIT_STATION)
 	var/hash = md5(SSmapping.config.GetFullMapPath())
 	if(CONFIG_GET(flag/generate_minimaps))
 		if(hash == trim(file2text(hash_path())))