Added support for liquid modifiers for both terrain (for using in oceans and seas) as well as a modifier for the new 'lakes' feature in which case lakes will be generated from that fluid (multiple fluids are supported for lakes but not for the ocean/sea)
Added liquid glowstone to the blacklist. We don't want oceans that flow upwards. Really, we don't.
Fixed a potential bug in biome selection where it would sometimes fail to select the right biome.
Implemented better random selection of modifiers in case no modifiers were specified.
Added None material and liquid dimlets to force no special generation for these modifiers.