modified: netbox_dns_bridge/signals/netbox_dns_zones.py
1. On zone deletion the catalog zone serial was not incremented, causing clients
not to delete the zone until another zone is created/modified. Fixed using
post_delete signal.
2. Even with the notify_clients feature disabled, the client IPs were still
being tracked. This disables the unnecessary behavior.
3. _track_seen_client function in DNSBaseRequestHandler did not have the 'self'
reference parameter, causing calls to fail. Fixed.