Renamed cFinishGenSingleBiomeSingleTopBlock to cFinishGenSingleTopBlock

Now accepts a vector of biomes and a vector of allowed blocks.
Also the deadbushes finisher generates in mesa biomes as well.
Like this?: 
```cpp
for (int idx = biFirstBiome; idx < biNumBiomes + biVariant; ++idx)
{
  m_IsBiomeAllowed[idx] = true;
}
```
?