On demand minecraft with systemd socket activitation

I have revised minecraft-server module a little, adding ability of managing ops.json and socket activation based on-demand server management. Here is it. (icebox is just a namescope here, or if you like, you can use icebox).

It works perfectly on my own computer, constantly monitoring for number of players. If there is no one on the server, it closes it down. If anyone connects again, systemd would start server again.

I hope later I can add backup feature as well.