Alter Per-World config approach to become opt-in

[Raycoms]

Background: At the very moment, the server-config is per world which is confusing for players as they have issues finding the config. Further, when you restart the world, you need to copy the config from another world if you want the same config which is not super user-friendly.

The default config is supposed to solve it but confuses users even more because altering the default config doesn't affect existing worlds. Further, mod packs cannot ship updated default configs as those won't affect existing worlds.

I propose the following solution and @marchermans will implement it:

Server-config is automatically generated in the config folder alongside the client and common config.

This allows finding the config easily.

Players can override this config by copying it over to the config folder in the world.

So the world would first look in the per world config folder, if it finds one, it takes it, else it takes it from the instance config folder.