set node fringe type in OSM import

[namdre]

If a road isn't tagged as dead-end we should assume it's fringe:

• https://wiki.openstreetmap.org/wiki/Key:noexit
• https://wiki.openstreetmap.org/wiki/Tag:highway%3Dturning_circle

[behrisch]

But if fringe goes from exception to rule, this should also apply to handmade / synthetic networks?

[namdre]

netgenerate already sets attachment edges to fringe=outer for grid networks.

[behrisch]

outer fringe should become the new default then

[behrisch]

Ideas for "dead-end" names are welcome (OSM name is noexit)