create submap containing air and roof tiles,

contains special handling to place roof on top of indoors tiles and stairs on top of stairs

make the starting shelter have a upwards stair to reach the roof
remove useless vector_has functions
remove last remnants of virtuality of map
add vehicle::smz to store the z-coordinate of the vehicles postion

similar to vehicle::smx, smy
not used in all places were it should be, that's on the TODO
port some more functions of map to use tripoints:

map::pl_sees, map::update_vehicle_list, map::determine_wall_corner

make the seen_cache 3D,
introduce MAPHEIGHT, which contains the maximal z-offset in both directions (currently 0, so effectively 2D only)

made map::light_at and map::pl_sees const functions