Refactor ‘finished’ to the model layer

By moving it from the view we reduce the complexity of the methods in
the view layer, so it’s easier to see what they do.

This also renames the variable `finished` to the property
`processing_finished` to disambiguate from the `job_status` field in the
JSON, which can also have a value of `finished`.

app/main/views/jobs.py

@@ -77,9 +77,6 @@ def view_job(service_id, job_id):
     filter_args = parse_filter_args(request.args)
     filter_args['status'] = set_status_filters(filter_args)
 
-    total_notifications = job.notification_count
-    processed_notifications = job.notifications_processed
-
     just_sent_message = 'Your {} been sent. Printing starts {} at 5:30pm.'.format(
         'letter has' if job.notification_count == 1 else 'letters have',
         printing_today_or_tomorrow()
@@ -87,7 +84,6 @@ def view_job(service_id, job_id):
 
     return render_template(
         'views/jobs/job.html',
-        finished=(total_notifications == processed_notifications),
         job=job,
         status=request.args.get('status', ''),
         updates_url=url_for(