Suggestion: accept auto_indexing=False in registration decorator

It would be nifty if `decorators.py`'s `register` ([definition](https://github.com/algolia/algoliasearch-django/blob/master/algoliasearch_django/decorators.py#L37)) accepted the same `auto_indexing` keyword argument as `registration.py`'s `register`.

See also #276 regarding `register` and `auto_indexing`.