Change default conversion reference from eciCMYK (FOGRA53) to eciCMYK v2 (FOGRA59)

[kimikage]

IIRC, the default conversion was based on eciCMYK (FOGRA53).
At the time I was coding it in 2021, it was early days when eciCMYK v2 (FOGRA59) was released, but now I see no reason to stay with eciCMYK.

Also, the internal model itself needs to be redefined since dark colors are poorly simulated.