Add poller group option for snmp-scan.py & config.php

Feature Requests
1

snmp-scan.py can be used to scan entire subnets, but cannot currently be configured to add specific subnets to certain poller groups. So 2 feature requests here.

  1. In config.php where you specify subnets to auto scan, allow us to specify what poller-group subnets should belong to
  2. Add a CLI argument option for specifying the poller group of a subnet we scan with snmp-scan.py