Development server: allow listening host other than "localhost"

[SlyEcho]

Background: Currently, the development server opens a socket on localhost:1990 by default.

While the port 1990 can be changed on the command line with -Dport=, there is no way to set the host IP/name.

Solution: I propose a build setting like -Dhost= or -Dlisten= or something similar for setting this option. It would accept a hostname or IP address.

Maybe it could even have some facility to listen on all addresses, but the user could also just use ::0 or 0.0.0.0 if that's desired, so this could just be mentioned in the help output / docs.

Motivation: it is useful for running the build server in a VM, or in some cases to check the built site on a mobile device, etc, without having to use port mapping or some extra work.