Feature Request: Option for the disabled_worlds list to function as a whitelist

[MemencioPerez]

For example, I have a server with the MythicDungeons plugin, which loads worlds on demand for each dungeon per player group. These worlds have the dungeon name followed by an underscore and a number, which makes it annoying to blacklist them. I already made a plugin for my server that listens for RoseStacker events to only allow stacking on specific worlds, but I think this would be a nice addition to the plugin for some servers.

I can make a Pull Request for that option if you agree to add it.