Shortcuts on traffic-calmed streets and private driveways

[dabreegster]

https://www.openstreetmap.org/way/1053284596 with highway=service, access=private, service=driveway probably shouldn't have any shortcuts. Actually, https://www.openstreetmap.org/node/10811300263 is a barrier=gate that should be blocking this right now, but I think we filter those out for some legacy reason... Revisit this.

https://www.openstreetmap.org/way/7997666 Willow Walk does have possible shortcuts, but there are several traffic_calming=humps like https://www.openstreetmap.org/node/10278959664 along it. So maybe it'd be useful to influence the shortcut calculation somehow, or at least visually indicate them.

Both of these are related to #51 -- technically a shortcut is possible, but properties of the road segment make it much less likely.

[dabreegster]

Users in Austria have reported that there are many access-only streets enforced with signage / trust, not barriers. From initial discussions, it seems like the route tool should still allow using these, but shortcut calculation should skip them. And we should communicate these cases both in tooltips on the road and visually on the map somehow.