Summary:
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}.

CCBUG: 359909

Test Plan:
Set up an ICC profile as described in D10076#197598 and open an
out-of-gamut image. Change the rendering intent in Gwenview's config
dialog, click {nav Apply} and observe that the image's colours change
immediately. Saving to the config file still works.

Reviewers: ngraham, muhlenpfordt

Reviewed By: ngraham

Differential Revision: https://phabricator.kde.org/D10187