Merge branch 'statistics_migrate' into 'dev'

stat part 1

See merge request !454

courses/models.py

@@ -77,6 +77,7 @@ class CourseManager(models.Manager):
                                 level=None, direction=None, **kwargs):
 
         slug = slug if slug else slugify(unidecode.unidecode(kwargs['title']))
+        old_slug = slug if old_slug is None else old_slug
 
         kwargs['teacher_tokens'] = teacher_tokens