Update letter data for usage-for-all-services report

Usage for all services is a platform admin report that groups letters by
postage. We want it to show `europe` and `rest-of-world` letters under a
single category of `international`, so this updates the query to do
that and to order appropriately.

app/models.py

@@ -1356,6 +1356,8 @@ SECOND_CLASS = 'second'
 EUROPE = 'europe'
 REST_OF_WORLD = 'rest-of-world'
 POSTAGE_TYPES = [FIRST_CLASS, SECOND_CLASS, EUROPE, REST_OF_WORLD]
+UK_POSTAGE_TYPES = [FIRST_CLASS, SECOND_CLASS]
+INTERNATIONAL_POSTAGE_TYPES = [EUROPE, REST_OF_WORLD]
 RESOLVE_POSTAGE_FOR_FILE_NAME = {
     FIRST_CLASS: 1,
     SECOND_CLASS: 2,