Use Vuokko’s bicycle edge traversal speeds (for Helsinki)

[christophfink]

@VuokkoH is right now deriving cycling speeds on the Helsinki street network, from the source we should not name.

Not quite sure whether we need changes to the Java code base, or whether this can be handled with the LADoT tags, i.e., without any special handling in R5 or r5py. Let’s still research the details for this

This does not technically belong here, but there might be an additional task: match the network of the bicycle speed data to any current OSM-derived network that we use in the analyses

[christophfink]

The first step is to add code to r5 to read a custom tag, and then use the speed read from the tag in bicycle routing