Normalized database. Updated seed files. Simplified seed upsert.

seeds/05_countries.js

@@ -1755,9 +1755,4 @@ const countries = [
 ];
 
 exports.seed = knex => knex('countries')
-    .then(async () => {
-        const duplicates = await knex('countries').select('*');
-        const duplicatesByAlpha2 = duplicates.reduce((acc, country) => ({ ...acc, [country.alpha2]: country }), {});
-
-        return upsert('countries', countries, duplicatesByAlpha2, 'alpha2', knex);
-    });
+    .then(async () => upsert('countries', countries, 'alpha2', knex));