Improve automatic emails with temporary urls

This MR targets the improvement for automatic emails concerning validation of new users by supervisors/re-validation of users.

Fixes #542 (closed)

Fixes #550 (closed)

beat/web/accounts/management/commands/clean_expired_temporary_urls.py

@@ -59,7 +59,7 @@ class Command(BaseCommand):
 
         temporary_urls_count = TemporaryUrl.objects.all().count()
         now = datetime.datetime.now()
-        count = TemporaryUrl.objects.filter(expires__lt=now).delete()[0]
+        count, _ = TemporaryUrl.objects.filter(expires__lt=now).delete()
         self.stdout.write('{} Expired temporary url(s) successfully cleaned/'.format(count) + '{} Total temporary url(s) checked'.format(temporary_urls_count))