Enable/Disable events for mail and DNS

[cuppett]

I'm sure most hosts utilize the domain creation, domain deletion events among others to power automation in a hosting environment with slave servers, mail firewalls, etc.; however, what would truly be useful would be to have events for when subservices such as mail and DNS are enabled/disabled. This way slave servers, mail gateways, among other dependent servers could be notified when these specific type of services are disabled.