fix 188 : make sure to spawn vehicles *on* the street

[Fusselwurm]

fix #188

fix: spawn vehicles to the side of the road, but make sure they're still on the road.

more todo:

• make sure the street is wide enough
• use actual vehicle width

[Fusselwurm]

use actual vehicle width

this turns out to be more effort than I'd like to. even boundingBoxReal offers veeery generous dimensions on some vehicles that are not better than me just assuming a vehicle width of 2m