Add UI to populate postgrey whitelist

Migrated from: https://tracker.clearos.com/view.php?id=17851

Reported by: Nick Howitt

The postgrey app has a whitelisting facility, achieved by populating /etc/postfix/postgrey_whitelist_clients.local then restarting postgrey.

I believe we ought to provide a UI to manipulate this file. We should be able to add IP addresses, subnets, FQDN's and regex's which describe FQDN's. It would be good to store a comment with each entry. As an example, my file looks like:

# Ebay
212.54.57.96/30

# PayPal.com
paypal.com
paypal.co.uk

# Clearcenter backup servers
clearsdn.com

# TPS - retries too quickly
212.250.30.21

# For Annie Jones
/^euk\d+\.eukhosting\.net/

# For Sony Playstation mta2.txn-email.playstation.com - mta9.txn-email.playstation.com
/^mta\d+\.txn-email\.playstation\.com$/

It is also possible to whitelist recipients in the /etc/postfix/postgrey_whitelist_recipients file but I don't think we particularly need to provide a UI for this.