Cleanup OD patterns

[dabreegster]

Today:

• from every origin to one destination
• from every origin to nearest destination
• from zone to zone
• from zone to point

Can we re-express this with less repetition?

Also, another pattern is commuting distance from an origin, without knowing direction

[dabreegster]

• [ ] Make the zone centroid fallback option (when no points match to a zone) consistently available everywhere
• [ ] Maybe use random intersections/graph nodes as a fallback option
• [ ] Warn clearly if the user hasn't provided inputs