Add missing grayscale conversions

Spread flakes out over 5 layers now (far back, mid distance, just behind land, just in front of lands and hog, near distance). Spread clouds out over 3 layers (far back, mid distance, just behind land). Add a flatten clouds option, use d on Underwater. Alter some flake PNGs to reduce variation in size since scaling is being used.

engine interaction class refactoring, round 4 or 5, can't remember: this time use the class methods to create an instance object and operates on that, reducing the number of arguments between methods and simplifying memory management

move two class files in a correct directory

exclude hogs from density check

too game breaking I think