remove warning (interia not allowed in base_footprint) and drag base_footprint down to the ground

- there was always a warning when launching that interia is not allowed in the basefootprint
- and we dragged the base_footprint down to the ground that there is at least one reference point a ground level. This is useful e.g. if you want to define a ROI for perception.

Can you also pick this to the master.