[Feat] Globally, unique city identifier

[franzos]

Problem:

• User's input / use local names (Lisbon, Lisboa)
• Cities may exist in multiple countries, and multiple times in one country? (Lisbon, Portugal / Lisbon, USA)
• Communities add their own cities (if any)

Example:

• User in Community A posts a property in "Lisbon,PT"
• User in Community B searches for properties in "Lisboa,PT"

Thoughts:

For Country and States we have ISO codes.

• Maybe a global index, all communities agree on?
• Format something like COUNTRY-STATE-CITYNAME