Treat a living_street as if it has a speed limit

[geozeisig]

Treat a living_street as if it has a speed limit of max 20 km/h.
Tag:highway=living_street: The implicit speed limits set in legislation vary from "walking speed" up to 20 km/h, in some countries, the speed limit is given explicitly on the sign.
If we don't do it that way, have to add maxspeed to every living_street.

[Florimondable]

duplicate of #238