[feature request] store maintenance on/off state in MySQL for game servers too.

[heathfx]

I have a case where I might need to command maintenance mode from a game server console directly rather than from the proxy. It would be nice if I could also take advantage of database sync on servers as well. I also can see using this on non-proxied servers as well. Like sandbox worlds that I provide for players. If I'm doing a series of restarts, I don't want them to get kicked multiple times from their test world if it happens to be on the same physical box as the main server and proxy...which for now everything is on the same box. I'll add this feature and submit a PR as soon as I have some time. just posting my request in case you can do it sooner.

an augmentation to this would be to make the maintenance plugin aware of physical hosts, so you can tell all nodes running on a certain box to enter maintenance mode.