Export: Add kind=Sidewalk to hw=path that we understand to be a sidewalk

Maybe related to #65

To my understanding the System already know that this `hw=path` is a sidepath, even though it is not tagged as such.
However, when exporting, we cannot filter it this way. I get the `kind=Sidewalk` on the generated ways, but not on those that we recognized as such.

https://a-b-street.github.io/speedwalk/#19/52.763256/13.244696

I expected the kind=Sidewalk on the `highway=path` but it its `kind=Other`.