Multicraft spesific shutdown.

Not sure if you are interested in this pull request as not everyone is using multicraft, but I thought since I made the change I could at least ask if you wanted it. I've only added a few lines of code that checks if the owner wants to use a multicraft spesific shutdown command.

The problem with a regular minecraft shutdown running under multicraft is that the server will just boot right up again, and that only makes matters worse if the disk is running dry.

Thank you for this simple but valuable plugin.