Add APIs to get: ISO and country name; geographic_region_id, g1name, g2name, g3name

Add 2 API methods for:
* getting the list of countries in GED (ISO, name)
* given a country ISO code, getting (geographic_region_id, g1name, g2name, g3name) for the studies available in the GED DB belonging to the given country.
Please add a comment to note that this approach is OK only because we know that we always have at least one study for each nation.  If this were not the case we would have to do a SELECT DISTINCT(iso) FROM ged2.geographic_region_gadm.