Separate World Gen into different respective terrain feature types

[muzikbike]

Currently everything is just lumped under "World Gen" without any consideration for what terrain feature it actually spawns as. Probably a better idea to split these up to distinguish between them better:

Mineral veins - what all ores spawn as, plus everything else mentioned in #238. Basically all of the stuff that generates underground replacing stone.

Disks - the circular patches found underwater. Clay is listed by the mod. Sand and gravel also spawn in this form, as does salt from mekanism if I remember correctly.

[way2muchnoise]

Interesting idea, would be feasible to implement. Maybe I can add some type of tag in the graph? It would however not work for the profiling feature (as I don't think I can make it aware of that).