Added a setting where the exported excel files should be stored.

Added a option to send the exported excel as mail attachment.

src/maistar_ranking/models.py

@@ -2,7 +2,7 @@
 
 import logging
 
-from django.core.urlresolvers import reverse
+from django.urls import reverse
 from django.db import models
 from django.db.models.signals import post_delete, post_save
 from django.utils.translation import ugettext as _