Biome ID settings to separate config file

[srs-bsns]

It might be prudent to separate the biome ID settings to another file. This way if a user wants to reset the biome IDs (automatically) they can do so by simply deleting the biome ID config file without having to delete the whole main config file. (Similar to how BoP separates their biome ID settings.)

The biome IDs should also be chosen automatically (if the config file doesn't exist), instead of using hard-coded defaults. This way, when Appalachia is initialised, there's no chance of a biome ID collision with IDs that have already been taken.

[whichonespink44]

So I've spent some time looking into this, and it seems that we can either register biomes with BiomeManager.addBiome() which allows you to set biome weights but not biome IDs... or we can use Biome.registerBiome() which allows you to set the biome ID, but not the weights.

Ideally, we want to be able to do both, but I'm not seeing a way to make that happen.