Add kerbs

[ginnyTheCat]

Adds kerb positions generated by muv-osm to osm2streets as discussed in #232 and tracked by #240. This provides a higher level of detail as it allows one to easily distinguish cycleway=lane from cycleway=track on the map.

It behaved quite unexpected for me for highway=cycleway + sidewalk=* but this is what the wiki suggests. In case this is unwanted we can skip the kerb in this case in every country but the Netherlands.

[dabreegster]

Thank you! I'll pick this up tomorrow. The rendering of the curb is a bit buggy; RenderLanePolygons.svelte probably needs a new case.

Relatedly, BufferType here can probably have an overhaul. I think https://wiki.openstreetmap.org/wiki/Proposal:Separation has caught on. I might have a go at some simple rendering for all of these cases. Downstream use cases might look at the quality of the separation of a cycleway from traffic.

[dabreegster]

Made some UI tweaks so it shows up, though really faintly. Thanks!