www/py-django-tables2: Assign to Django 2.2

• Because Django 1.11 is End-of-Life since April 2020 thus switch over to Django 2.2 which is the current LTS release.

• Set the minimum required Python version for Django 2.2 accordingly and bump PORTREVISION for changed dependencies.

• Mark the repo-copied port www/py-dj22-django-tables2 as DEPRECATED because it's obsolete now. Don't set an expiration date yet as it's still used by net-mgmt/netbox and a few more Django 1.11 ports need to be assigned to Django 2.2 first.

• Also update the CONFLICTS_INSTALL entries as the repo-copied port py-dj21-django-tables no longer exists in the Ports tree.

PR: 245309