Patch from issue 1359: "Munsell correction - Lab adjustements" credits: jdesmis

Bundled new features besid the Lab tool enhancement (by jdesmis) :
   - curve to control skin tones in vibrance tool, credits: jdesmis
   - right click over SHCSelector (below the parametric curve) to reset to default values, credits: Hombre
   - colored bars around curves, credits: Hombre

rtgui/options.h

@@ -238,6 +238,7 @@ class Options {
     Glib::ustring lastLabCurvesDir;
     Glib::ustring lastHsvCurvesDir;
     Glib::ustring lastToneCurvesDir;
+    Glib::ustring lastVibranceCurvesDir;
     Glib::ustring lastProfilingReferenceDir;
 
     Options ();