Update config templates to Havana release

Use upstreams password-validator configuration.

Don't set SESSION_ENGINE to cached_db but rather use upstream's default
(signed_cookies). This way, Django's session backend doesn't access the
database anymoe. The table "django_sessions" could stay in the DB if
present, it doesn't hurt.

COMPRESS_OFFLINE is not needed on SUSE anymore after upstream moved to
python-lesscpy (instead of nodejs / lessc).