Configure world generation on world creation screen

[WrongWeekend]

A number of other world generation mods allow players to customize the world generation parameters in-game as they create a world. Such a feature for this mod would be very helpful for experimentation with the amount of customization options that it offers. The existing config files and settings could be used as the default settings on the in-game customization interface.

[valoeghese]

Wouldnt be too hard to implement I think, though we'll wait for the terrain gen rewrite before starting this