Put counts into the notification filters

We can filter notifications on the activity page by state.

This commit adds counts to those filters.

This is mainly so that we can consistently do the same thing on the job
page later on.

app/statistics_utils.py

@@ -48,3 +48,24 @@ def add_rates_to(delivery_statistics):
         ),
         **delivery_statistics
     )
+
+
+def statistics_by_state(statistics):
+    return {
+        'sms': {
+            'processed': statistics['sms_requested'],
+            'sending': (
+                statistics['sms_requested'] - statistics['sms_failed'] - statistics['sms_delivered']
+            ),
+            'delivered': statistics['sms_delivered'],
+            'failed': statistics['sms_failed']
+        },
+        'email': {
+            'processed': statistics['emails_requested'],
+            'sending': (
+                statistics['emails_requested'] - statistics['emails_failed'] - statistics['emails_delivered']
+            ),
+            'delivered': statistics['emails_delivered'],
+            'failed': statistics['emails_failed']
+        }
+    }