Footway/Service road permissions

[spencerrecneps]

Allows bicycle use on footways and service roads where bicycle tag is "yes", "permissive", or "designated".

[spencerrecneps]

These changes mimic the changes made here:
azavea/pfb-network-connectivity#785

@beckymasond one thing I wanted to run past you. In the original code I had a constraint that only allowed footways to be used if they were explicitly tagged at least 8 feet wide. I carried this through in pybna, but this dramatically reduces the footways that get assigned as paths. I've removed the width constraint in this PR, which I think matches the current practice in the production BNA system.

The intent behind the width constraint, as well as only allowing bicycle=designated, was basically to prevent sidewalks from being credited for bike connectivity unless the sidewalks are very wide and explicitly included in the bike network.

Do you have thoughts about this? I can reintroduce if you want something in there.

[beckymasond]

The main goal of expanding the footway and service tags was to ensure that the value "yes" is considered acceptable like "designated," since users brought me instances of service roads and footways that are bike-friendly being left out of the analysis for that reason and it caused some confusion. I left the width requirement in the functional_class script in the original BNA so it still retains that stringency, and I agree that it makes sense to leave that width requirement in for the reasons you mentioned.