pidstore: provider status sync and celery tasks
- Adds feature to synchronize the status of a persistent identifier with the provider. Useful for cases where the status of an identifier might have been modified in an external service.
- Adds namespace prefix to configuration variables.
- Adds celery tasks to registering DataCite DOIs for records.
- Fixes some PEP8 errors.
Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>