Away mission preparations.

Created by: ComicIronic

Added the addZLevel proc, used to sanitize map init and generate the accessable_z_levels list, which is no longer hardcoded. Fixed a couple of maps I ended up using in testing. Added more debug data to a debug verb for maps. Added the movementJammed var, which stops a zlevel being reachable by drift. Added the movementChance var, which controls how likely a zlevel is to be reached by drifting. Made the maploader add any new zlevels it creates to the map's zlevel list.