Merge/integrate with `django-q2`

[joshuadavidthomas]

At some point when the API of this package has stabilized, it might be worth it to make an issue in the actual django-q2 project about moving the functionality of django-q-registry within the package itself rather than keeping it separate.

Offering some sort of automatic task discovery is a semi-standard feature across other django task runners and there is a stale open issue about it.