MWEB-979 Watcher and server runner

@RafLeszczynski @hakubo Please check if workaround in `gulp/options/dev.js` is acceptable. It worked fine while smoke tested.
I believe this method is better because the server is restarted just as the building task is finished. I wouldn't want to introduce a race condition that can fail if machine is being slower at the moment. Both solutions are workarounds but this here looks more reliable for me.