Make no-nether world message configurable

[tomhula]

Feature request

Feature description
Make no-nether message configurable in config. When you enter a nether portal, which doesn't lead anywhere, it says: "This portal goes nowhere". And I think, it would be good, if you could configure this message in config.

How the feature is useful

1. You can translate the message to your language.
2. You can format it to fit your servers style.