Add a geocoding option

[cholmes]

Right now you have to input a geojson - it'd be much nicer for many users to just enter like a city, state or county name and get buildings for it.

Ideally we find a geocoder that returns polygons, and doesn't cost too much. I could likely pay for it for a bit, but we probably evolve to making it a config option for people to put in their geocoder api key.

[mtravis]

@cholmes i think we could use the OSMnx python library for this.https://osmnx.readthedocs.io/en/stable/getting-started.html#geocoding-and-querying

I've got scripts that use it that I can adapt so I'd love to work in this one.

[cholmes]

Awesome - I'm open for any approach, and free solution sounds great.