Add a FixtureConnector

[ZuluPro]

The primary solution before solutions like DBBackup is dumpdata/loaddata. I don't like it because serialization/deserialization take time. But it can be useful to migrate DB across environment, example: a production in Postgres and testing in SQLite.

I think about a FixtureConnector allowing to dump and restore with Django built-in features and working with DBBackup mechanisms (encryption, compression, uploading).

[iosifnicolae2]

@ZuluPro https://github.com/django-dbbackup/django-dbbackup/pull/309 might be useful