- add celery application code in gvaldap.celery
- add osusers app to mimic the osusers code in the main gnuviechadmin code
- add celery configuration settings to gvaldap.settings.base
- add osusers.models.Group and osusers.models.User
- add osusers.tasks.create_ldap_group and osusers.tasks.create_ldap_user
- add billiard, kombu and pytz to requirements/base.txt