add normalised country name to word table

Country tokens now follow the usual convetion of having the
normalized version in the word column and the extra info about the
country code in the info column.

src/nominatim_api/search/query.py

@@ -127,6 +127,12 @@ class Token(ABC):
             category objects.
         """
 
+    @abstractmethod
+    def get_country(self) -> str:
+        """ Return the country code this tojen is associated with
+            (currently for country tokens only).
+        """
+
 
 @dataclasses.dataclass
 class TokenRange: