python3-django package has been upgraded to version 2.2 in debian unstable.

Unfortunately, the package python3-django-js-reverse needed by swh-web is not compatible
with Django 2 in its current state as the packaged version is 0.7.3.

The upstream version of django-js-reverse is 0.9.1 and is compatible with Django 2 so we
need to backport it in order to be able to successfully build swh-web packages.