GalleryProcessors do not convert images with CMYK and YCCK color model to RGB before scaling and they should

Current situation

The org.hippoecm.frontend.plugins.gallery.processor.AbstractGalleryProcessor does not convert images with a CYMK color space and YCCK image model to RGB and it should, because CMYK and YCCK require another gamma and the ImgScalr. library does not perform a gamma correction for these image models and RGB is more suited for display on monitors.

Various color model require a different gamma.

Desired situation

During processing the image variants the color model is converted to RGB and then the scaling and cropping operations are performed. The org.hippoecm.frontend.plugins.gallery.imageutil.ImageUtils#convertToRGB method can be used.

I guess CMS-6077 will be resolved as well if we implement this change.