Add enabled_worlds option

[Nuytemans-Dieter]

Describe the new feature you have in mind

hello, I have a server where for each event that there is I create a new world and it is very tedious to be adding that new world to the list of disabled worlds. I would like the enabled worlds to be specified in the configuration which is actually only 1 for my case: world

Maybe make it so it can be changed from a blacklist to a whitelist at will. So it stays plug and play. Then if you only ever want one world then you can change it to a whitelist and add only that world.

[Nuytemans-Dieter]

Configuration should remain easy, keeping this issue on hold for now until a simple implementation is possible