runners/datetime: Proper city search

Adds a database of city names and timezones sourced from geonames.org, filtered for population >400k. File is ~44 KB.

Test Plan

Try searching for: time delhi, time mumbai, time beijing, time new york, time seattle, time san francisco, time berlin, time montreal, time montréal, and so on. The theme being major cities which may not happen to have their name in a timezone id.