Add a command for changing configuration in-game

[WerDei]

Some people prefer configuring mods in-game rather than edit a text file.

This would mean rewriting a good chunk of a config loader to allow adding and removing rules on the fly. I'd love to keep any commented lines in the file intact somehow too, if possible.

Since world needs to be closed and loaded again for changes to take effect, player needs to be informed about that after using this command.