Add a selective restart Make target

I often find myself run make down-<svc> up-<svc> to restart a single service.

This MR ties these two together into a restart-<svc> target.

Say you run make web, but then only want to restart workhorse. You can now do that with make restart-workhorse; when it comes back up, it will print to the same console window into which you had initially run make web, which is convenient.

The alternative is to make env and then in the repl, use docker-compose restart <svc>, but that is less convenient.