Issue 2846: Filter preview through output profile when using a monitor profile.

- Removed the "Rendering intent" setting from Preferences,
- Hard-code "relative colorimetric" intent everywhere,
- Filter through output profile before filtering through monitor
  profile if using a monitor profile,
- If not using a monitor profile, a direct sRGB conversion is done,

rtengine/stdimagesource.cc

@@ -279,7 +279,7 @@ void StdImageSource::colorSpaceConversion (Imagefloat* im, ColorManagementParams
         }
 
         lcmsMutex->lock ();
-        cmsHTRANSFORM hTransform = cmsCreateTransform (in, TYPE_RGB_FLT, out, TYPE_RGB_FLT, settings->colorimetricIntent,
+        cmsHTRANSFORM hTransform = cmsCreateTransform (in, TYPE_RGB_FLT, out, TYPE_RGB_FLT, INTENT_RELATIVE_COLORIMETRIC,
                                    cmsFLAGS_NOOPTIMIZE | cmsFLAGS_NOCACHE);
         lcmsMutex->unlock ();