Biome managing in World + addition in PluginLoader

Added a BiomeGenBase wrapper, we might not need it after all,
it's not implemented in NMS yet at any rate.

PluginLoader will now try to look up Plugins from disk,
when enabling the, to allow enabling of newly added Plugins.

World now contains setBiometype and getBiometype.
Generally the whole biome data array can still be obtained from Chunk