Add functionality to change Apache VirtualHost definitions from UI

A use case exists where Aegir-managed websites exist on an Apache web server along with static virtual hosts. The static host definitions begin like...

<VirtualHost 192.168.1.10:80>

whereas current aegir-managed virtual host definitions look similar to...

<VirtualHost *:80>

This mix of wildcard and specific IPs can cause issues in Apache's ability to send traffic to the correct virtual host. It would be nice if the aegir UI allowed control over this functionality.

A text field to specify an IP would be easy, but I think it'd be a little more slick if you could define IPs available on a server, then in the site definition you select one or more IPs either from a drop-down or field of checkboxes (with * as a default option, probably)