now that we're reading from two tables (ft_notification_status and
notifications) for stats, we'll get a couple of rows for each
notification type. If a service doesn't have any rows in one of those
tables, the query will return a row with nulls for the notification
types and counts. Some services will have history but no stats from
today, others will have data from today but no history.
This commit acknowledges that any row might have nulls, not just the
first row.
Added cancelled letters to the number of failed letters in the statistics
that get used for the dashboard. At some point, we want to stop
including cancelled letters in the stats, but for now this keeps things
consistent with our current letter failure state, permanent-failure.
Added in a new endpoint and DAO function to provide the data for the new
platform admin statistics page. The DAO method gets different data from
the Notifications / NotificationHistory table and also groups it differently.
The old endpoint has not been deleted yet to allow the numbers on the
old and new pages to be compared.
moved format_statistics to a new service/statistics.py file, and
refactored to share code. moved tests as well, to try and enforce
separation between the restful endpoints of rest.py and the logic/
data manipulation of statistics.py
