Improved mipmaps

This MR improves performance of mipmap generation and quality.

It also uses limear mipmaps, they are far more bautiful. The mipmap code is taken from here: https://bugs.mojang.com/browse/MC-114265

I still need to clarify under what license it is.

ToDo:

• Mipmap usage in everything else except world renderer
• Use 3 meshes (and shaders) per renderer: Opaque, Transparent, Translucent
• Test
• Test mixing transparent and translucent
• Improve transparent rendering