Added new color toning method "L*a*b* regions"

Allows to specify various "regions" of the image with masks, and to correct
for hue, saturation and lightness.

Inspired by the existing L*a*b* grid (in turn taken from darktable)

rtengine/improccoordinator.cc

@@ -717,6 +717,7 @@ void ImProcCoordinator::updatePreviewImage(int todo, bool panningRelatedChange)
             histLCurve.clear();
             ipf.chromiLuminanceCurve(nullptr, pW, nprevl, nprevl, chroma_acurve, chroma_bcurve, satcurve, lhskcurve, clcurve, lumacurve, utili, autili, butili, ccutili, cclutili, clcutili, histCCurve, histLCurve);
             ipf.vibrance(nprevl);
+            ipf.labColorCorrectionRegions(nprevl);
 
             if ((params.colorappearance.enabled && !params.colorappearance.tonecie) || (!params.colorappearance.enabled)) {
                 ipf.EPDToneMap(nprevl, 5, scale);