Pavement solution for 3D buildings.

map.xml:
Object type "pavement" introduced.
Only one building and one pavement are available with a closeby spawning
point. The pavemnt extends the building with 1 meter in all directions.
The original map is saved in map_backup.xml

Function draw in building2d:
One code snippet for drawing the footprint of a gemetry. Usable for
pavement.
One codesnippet for drawing fake 3d buildings.