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.
Any chance of getting all these into a simple array, to make the code shorter?
```cpp
cStructGenOreNests::OreInfo Veins[] =
{
  {E_BLOCK_DIAMOND_ORE, 15, 1, 4},
  {E_BLOCK_LAPIS_ORE,   30, 2, 5},
  ...
}
```