Store CMYK profile in GimpImage when loading TIFF
This merge request adds gimp_image_set_simulation_profile ()
to retain the CMYK color profile when loading CMYK TIFFs. The profile is stored in GimpImage, and will be accessible to the user via the Image > Color Management menu.
To facilitate this, the command to clear out the CMYK profile is moved from when space
is initialized to after the image is created (right above the existing code to store the color profile if it's RGB).
The profile saving code is similar to what is used in !646 (merged)