Add Service.get_days_of_retention helper method

Data retention lookup by type is only performed to get the number
of days, so we can update the service method to return the number
or the default directly.

app/main/views/jobs.py

@@ -3,7 +3,6 @@
 from flask import (
     Response,
     abort,
-    current_app,
     jsonify,
     redirect,
     render_template,
@@ -226,9 +225,7 @@ def get_notifications(service_id, message_type, status_override=None):
     service_data_retention_days = None
 
     if message_type is not None:
-        service_data_retention_days = current_service.get_data_retention_by_type(
-            message_type
-        ).get('days_of_retention', current_app.config['ACTIVITY_STATS_LIMIT_DAYS'])
+        service_data_retention_days = current_service.get_days_of_retention(message_type)
 
     if request.path.endswith('csv') and current_user.has_permissions('view_activity'):
         return Response(
@@ -406,9 +403,7 @@ def get_job_partials(job, template):
             counts=_get_job_counts(job),
             status=filter_args['status']
         )
-    service_data_retention_days = current_service.get_data_retention_by_type(
-        template['template_type']
-    ).get('days_of_retention', current_app.config['ACTIVITY_STATS_LIMIT_DAYS'])
+    service_data_retention_days = current_service.get_days_of_retention(template['template_type'])
 
     return {
         'counts': counts,

app/main/views/notifications.py

@@ -8,7 +8,6 @@ from dateutil import parser
 from flask import (
     Response,
     abort,
-    current_app,
     jsonify,
     render_template,
     request,
@@ -197,9 +196,7 @@ def download_notifications_csv(service_id):
     filter_args = parse_filter_args(request.args)
     filter_args['status'] = set_status_filters(filter_args)
 
-    service_data_retention_days = current_service.get_data_retention_by_type(
-        filter_args.get('message_type')[0]
-    ).get('days_of_retention', current_app.config['ACTIVITY_STATS_LIMIT_DAYS'])
+    service_data_retention_days = current_service.get_days_of_retention(filter_args.get('message_type')[0])
     return Response(
         stream_with_context(
             generate_notifications_csv(