MZ Fixes (#4936)

changes:

Fixes a regression in GetAbove/GetBelow() that caused passing an atom that wasn't directly on the map to return a false negative.
Fixes runtime's broken Z1 MZ by moving it to Z2.
Fixes some outdated Z-level defines on Runtime.
Moves z_levels global to SSatlas for easier debugging.
Atlas will now list the size of the world in its MC entry.
Map diffs are fucked up because of the index shift, nothing on the maps themselves was actually changed beyond adding a blank Z at the bottom.

Fixes #4692.

code/controllers/subsystems/initialization/atlas.dm

@@ -18,6 +18,10 @@ var/datum/controller/subsystem/atlas/SSatlas
 	var/list/spawn_locations = list()
 
 	var/list/connected_z_cache = list()
+	var/z_levels = 0	// Each bit represents a connection between adjacent levels.  So the first bit means levels 1 and 2 are connected.
+
+/datum/controller/subsystem/atlas/stat_entry()
+	..("W:{X:[world.maxx] Y:[world.maxy] Z:[world.maxz]} ZL:[z_levels]")
 
 /datum/controller/subsystem/atlas/New()
 	NEW_SS_GLOBAL(SSatlas)
@@ -112,6 +116,7 @@ var/datum/controller/subsystem/atlas/SSatlas
 /datum/controller/subsystem/atlas/proc/setup_multiz()
 	for (var/thing in height_markers)
 		var/obj/effect/landmark/map_data/marker = thing
+		log_debug("atlas: setting up Z marker on level [marker.z] with height [marker.height].")
 		marker.setup()
 
 	connected_z_cache.Cut()