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/models/job.py

@@ -83,10 +83,13 @@ class Job(JSONModel):
     @property
     def still_processing(self):
         return (
-            self.status != 'finished' or
-            self.notifications_created < self.notification_count
+            self.status != 'finished' or self.percentage_complete < 100
         )
 
+    @cached_property
+    def finished_processing(self):
+        return self.notification_count == self.notifications_processed
+
     @property
     def template_id(self):
         return self._dict['template']