Build world-specific configs

[Roundaround]

Build out a world-based config system. When not inside a world, the config menu will modify the global config, which will serve as the default for any world that doesn't have its own. Likewise when in a world, the menu will modify a file within the world's directory.

More or less a prerequisite for #4, because tags work similar to datapacks in that they are world-specific.