Make django-binary-database-files standalone

[rhunwicks]

This verison of django-database-files was forked from https://github.com/bfirsh/django-database-files via https://github.com/chrisspen/django-database-files-3000 and https://github.com/rhunwicks/django-database-files and the changes made to use native binary fields instead of uuencoded text files we kept outside the master branch to ensure continued compatibility with upstream.

However, none of the upstreams are particularly active and so we will make this a standalone repo.

Consquently:

• we will rename this repo to django-binary-database-files and then publish a PyPI package under the same name
• we will open up Issues on this repo
• we will merge our changes to master and update it for modern Python and Django
• we will set up CI for this repo against currently supported Python and Django versions