www/py-django-tables2: Update to 2.3.1

• Add option TABLIB to reflect the optional dependencies as noted via setup.py. Also set the option as non-default for now because it pulls in a large set of dependencies and the port runs fine without them.

• Remove stale CONFLICT_INSTALLS entry.

Changelog:

https://github.com/jieter/django-tables2/blob/v2.3.1/CHANGELOG.md