New port: www/py-dj22-django-auth-ldap

Repo-copy www/py-django-auth-ldap and assign it to Django 2.2 to enable LDAP
authentication with net-mgmt/netbox that has been switched to Django 2.2 in
r502550 .

Also limit the port to Python 3.5+ as Django 2.2 requires it as minimum
dependency and update all related CONFLICTS_INSTALL entries.