This commit reorganizes the package structure. The gvaldap.settings
modules have been merged. The gvaldap.ldaptasks module has been move up
one level to have task names without the gvaldap prefix.
isort control instructions have been added to setup.cfg.
All LDAP tasks return a dictionary now to allow chaining with other
tasks, the new task delete_ldap_user_chained has been added to allow
user deletion after other Celery tasks.