Add configurable Biome Key format

[OakLoaf]

I need opinions on:

• Whether the format should be in the config.yml or should be individually configurable per pack.
• Should we add a warning message above the config option that changing it will require a world reset?

I've only implemented this for the bukkit platform currently whilst we discuss how the overall implementation should be structured

[ItsJuls]

I think it should be configurable per pack or so for customization like each biome has its own unique biome key format