Adds a toggle for monstermos doing planet decomp (off by default)

code/controllers/subsystem/air.dm

@@ -61,6 +61,8 @@ SUBSYSTEM_DEF(air)
 	var/share_max_steps = 3
 	// Excited group processing will try to equalize groups with total pressure difference less than this amount.
 	var/excited_group_pressure_goal = 1
+	// If this is set to 0, monstermos won't process planet atmos
+	var/planet_equalize_enabled = 0
 
 /datum/controller/subsystem/air/stat_entry(msg)
 	msg += "C:{"