Optionally hide tunnels

[dabreegster]

https://a-b-street.github.io/osm2streets/#17.29/51.513285/-0.088692

Bank station's pedestrian tunnels are all mapped. Since z-ordering between layers in maplibre is hard/impossible, street explorer lacks z-ordering, and this area looks like a mess. For this edge case, I think it'd be helpful and simple to have a filter for layer. Could just be client-side, since it's already plumbed back