This is a follow-up patch to D10076, so after changing the rendering
intent in Gwenview's config dialog the displayed image is updated
immediately after clicking on {nav OK} or {nav Apply}. Before, it was
necessary to {nav Reload} the image manually or pan around.
Currently this is only implemented for raster images. In case someone
figures out colour management for SVGs, this patch should be extended to
SVGs too.
Depends on {D10076}.