Added an extra step to classify service roads as running through a
parking lot, to prevent them from being treated as regular roads.
Had to fix up a few prebaked traffic signals. lakeslice falls back into
gridlock; will fix separately -- too much effort behind this change to
stop.
Originally it was split out to organize a separate volunteer mapping
effort, but that never took off, and it's unlikely to happen. When we
have to occasionally update the prebaked signal data for some
intersections, it's unnecessary friction to update the other repo.
