Some new script commands

I added three new script commands.

/players lists all online players with their locations.

/maps lists all active map instances with their player count and mob count.

So far, so boring. But the really powerful command I added is the /shell command. It allows to execute Javascript code on the server. So it can do virtually anything. This powerful tool will allow me to analyze and fix a lot of problems on the running server on-the-fly as well as do complex events. It is also extremely dangerous in the wrong hands and I see no way to add permission-based restrictions to it, so I definitely need to shield this command from unathorized use. I will also not use the existence of this command to refrain from adding more commands which do things which could theoretically also be done with /shell, so I won't be tempted to give the /shell command to people I don't trust 110%.