Add downloadable report for org usage

This is so org level users can use this data easier for things
like determining spending per service.

We do not include sms fragments sent column and remove other sms columns

consistency.

Do not add sms fragments sent column for now until we agree on an
unambiguous name for it. The data in this column is sms billing units
multiplied by international sms weighing. My favourite for a clear
name would be 'text message credits used', but we need a naming
strategy for this.

tests/app/test_navigation.py

@@ -89,6 +89,7 @@ EXCLUDED_ENDPOINTS = tuple(map(Navigation.get_endpoint_with_blueprint, {
     'documentation',
     'download_contact_list',
     'download_notifications_csv',
+    'download_organisation_usage_report',
     'edit_and_format_messages',
     'edit_data_retention',
     'edit_organisation_agreement',