server: use JS location.hostname with livereload.js resource

[blueyed]

Uses JavaScript to dynamically inject the client's hostname.
This allows for serving on 0.0.0.0, where a rendered hostname of
"0.0.0.0" would not resolve necessarily to the server's address.

[RonnyPfannschmidt]

i recall that modern livereload.js can extract those information on its own,
it might be worth a try to leave its discovery to itself

[blueyed]

@RonnyPfannschmidt

i recall that modern livereload.js can extract those information on its own,

But it needs to be loaded first?!

If there's http://0.0.0.0:$port/livereload.js in the HTML on a remote client, how should it get retrieved from e.g. 192.168.X.X?