[Post-processing] logic rework, cleaning, & prelim shader code for palette textures.

Just tidied up the code, reworked some logic for the tone mapping, sharpening, and scaling. Also adding the preliminary shader code for palette textures. I still have to do the code for the annotations yet though.

Example screenshot of the tone mapping & bloom with demo settings in Divinity: OS here: https://flic.kr/p/pNgf8e