(Request) Send SIGHUP to load changes

[outlyer-net]

This has probably more to do with webproc than with this container but I think it would be great to have the webinterface send a HUP signal after saving changes.

It's currently sending an INT signal, waiting, killing the process, waiting and then relaunching dnsmasq, which is fairly slow.

However sending a HUP signal reloads the configuration immediately, e.g.:

$ docker exec dnsmasq killall -HUP dnsmasq