Merge branch 'statistics_migrate' into 'dev'

stat part 1

See merge request !444

lms/celery.py

@@ -25,7 +25,7 @@ app.conf.beat_schedule = {
         'task': 'finance.tasks.periodic_billing'
     },
     'statistic_teachers': {
-        'schedule': crontab(minute='*/2'),
+        'schedule': crontab(hour='16', minute='0'),
         'task': 'progress.tasks.statistic_teachers'
     }
 }