Use client-side host for generating dashboard request URLs

I explained my motivation for this change on [Taffy Users](https://groups.google.com/d/msg/taffy-users/kh3QeKY4F3o/bHvzWBfyA8gJ).  Basically my CGI.SERVER_NAME was not a resolvable name and so I'm swapping server-side logic for client-side.