Backporting patch from issue #3446

This commit change the way that the Curve buttons and Accompanying
object expands, and fix the alignment of the WB's buttons.

rtgui/curveeditorgroup.h

@@ -85,7 +85,7 @@ public:
         return displayedCurve;
     }
     //void on_realize ();
-    CurveEditor* addCurve(CurveType cType, Glib::ustring curveLabel, Gtk::Widget *relatedWidget = nullptr, bool periodic = true);
+    CurveEditor* addCurve(CurveType cType, Glib::ustring curveLabel, Gtk::Widget *relatedWidget = nullptr, bool expandRelatedWidget = true, bool periodic = true);
 
 protected:
     //void curveTypeToggled ();