Break down usage by month, filter by year

The previous, weekly activity breakdown was what we reckoned might be
useful. But now that we have people using the platform it feels like
aggregating a service’s usage by month is:
- matches the timeframe users report on within their organisation
- is consistent with the usage page

And like the usage page this commit also limits the page to only show
one financial year’s worth of data at once (rather than data for all
time).

This commit also makes some changes to the jobs view code so that our
aggregation of failure states is consistent between the dashboard pages
and the jobs pages.

app/utils.py

@@ -32,6 +32,12 @@ import pyexcel.ext.xlsx
 import pyexcel.ext.ods3
 
 
+SENDING_STATUSES = ['created', 'pending', 'sending']
+DELIVERED_STATUSES = ['delivered']
+FAILURE_STATUSES = ['failed', 'temporary-failure', 'permanent-failure', 'technical-failure']
+REQUESTED_STATUSES = SENDING_STATUSES + DELIVERED_STATUSES + FAILURE_STATUSES
+
+
 class BrowsableItem(object):
     """
     Maps for the template browse-list.