Refactor to core

In order to make the preview window work I had to create an extra lifecycle step in the world generator interface to allow world generators to get partially created (so that the biome stuff could get created without accessing blocks).  Also,  because modules do not get officially enabled until the world staring process has begun, I had to hack in enabling/disabling the module containing the world generator so it would actually create the object and allow the preview data to be retrieved.