update requirements.txt : add celery
add celery module
update requirements.txt : add django-celery
update settings.py : add djcelery in INSTALLED_APPS
update settings.py : django-celery setting for DB
fix settings.py : import should be on the top
Merge branch 'feature/integrate-celery' into develop

* feature/integrate-celery:
  fix settings.py : import should be on the top
  update settings.py : django-celery setting for DB
  update settings.py : add djcelery in INSTALLED_APPS
  update requirements.txt : add django-celery
  add celery module
  update requirements.txt : add celery
Merge pull request #21 from dobestan/develop

[Sprint #4] Integrate with Celery