Ore Tweaks

Added `NetherOreNests` generator. It generates nether quarts.
Added `NaturalPatches` generator. (I'm not sure if I like the name) It generates dirt and gravel.
The `OreNests` generator now only generates ores.
It's not exactly needed; the performance gains are negligible (and it's not a place to be concerned about performance anyway, it's a one-time initialization); it just improves readability, imho.