Assign every place a country code

It would be ideal if each source dataset contained the ISO country-code for each place, unfortunately, this is rare.

This issue is to investigate a method of ensuring that each place is associated with an ISO code at import-time.

One way this could be achieved is to enforce hierarchies for each place and use that to find the country.

Another way would be to PIP each place as it's imported, but this comes with the complexity of requiring countries (and dependencies) to be imported prior to other data.

We could also consider relaxing the requirement to say that the country code is allowed to be NULL during import but is computed later, after all the data imported via a post-processing script. -it depends on how we intend to use it.

Some advantages to having mandatory country codes:

• Issues like https://github.com/pelias/spatial/issues/4 can be resolved
• Fast filtering and searching per-country
• Easy to cut regional extracts from a planet database
• etc.

We would also need to develop a convention for places for which an ISO code is not relevant, just as: ocean, continent, planet

No file, test, or entry point is named. Start by locating the import pipeline and how place hierarchies and country data are represented. Done requires a chosen import or post-processing approach, ISO codes for places where applicable, and a convention for places such as oceans, continents, and planets.