country_name: use separate columns for names from OSM

This allows us to distinguish between base names and imported ones
and consiquently removing imported ones if necessary.

data/country_name.sql

@@ -5,6 +5,7 @@
 CREATE TABLE public.country_name (
     country_code character varying(2),
     name public.hstore,
+    derived_name public.hstore,
     country_default_language_code text,
     partition integer
 );