Adds a new world type to the create world screen, the Amplified-Mixed Type.

This world type rolls Regular Worlds, Large Biomes, and Amplified Terrain into one (slow) world type.

• In Large Biome Worlds, the biomes are 8 times larger, in Amplified-Mixed, its only 4.
• In Amplified worlds, all terrain (above the sea level) is doubled in height, (as well as some other things that create the overhangs and whatnot), in Amplified-Mixed, it only occurs in around about half the world.