Balance Cave Update

From what I've seen its pretty easy to get diamonds with this new cave update! Its urgent to balance the game in order to "have the need" to have some challenge when progressing through the game resourses.

Simples basic ideas:

- make visible diamond more rare;
- make iron ore appear below copper, or at least not so near the suface;
- fix water doors cheating, where you can put doors underwater in order to breath. Under this new terrain generation you have large lakes and rivers that go newr bedrock so its easy to reach the bottom levels;
- Make villages more rare and improve their looting quality;