The task `deploy:restart` was doing nothing since we moved from unicorn
to puma.
Now we're also restarting delayed jobs on `deploy:restart`, which is
probably what's expected in most cases.
Puma is the server we use in the development environment, so this way we
don't need to maintain two servers. Furthermore, puma seems to offer a
few advantages over unicorn (like multithreading) and no disadvantages.
