Replaced the outside turfs with exoplanet ones for the digsite.
Fixed some exoplanet areas not having an exoplanet base turf.
Wrote a unit test for exoplanet areas to ensure they have an exoplanet
base turf.
Adds lava interaction: humans walking on lava titles will suffer a slowdown then being set on fire, cyborgs and simple mobs will only take burn damage.
Added the lava and basalt turfs to a random map generator, and replaces the tundra's ocean with the title just named water.
Created a global list to track base turfs for explosions/shuttle moves.
Remaps the asteroid to be a moonlet. Tidies up some references to 'asteroid', removes moonbase from the accessible z level list.
