This commit updates the Django dependency version to 1.9.2 and gvacommon
to 0.3.0 that provides gvacommon.settings_utils.get_env_variable. The
gnuviechadmin.settings.base module now uses this implementation instead
of an own copy and the corresponding test has been removed too.
- 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