add feature that mupp_plotter can show/hide lines between the data points.

src/musredit_qt6/mupp/plotter/PMuppCanvas.h

@@ -46,8 +46,9 @@
 #include "mupp.h"
 
 // Canvas menu id's
-#define P_MENU_ID_EXPORT 10001
-#define P_MENU_ID_ABOUT  10002
+#define P_MENU_ID_WITH_LINE 10001
+#define P_MENU_ID_EXPORT    10002
+#define P_MENU_ID_ABOUT     10003
 
 //--------------------------------------------------------------------------
 struct PDataPoint {
@@ -113,6 +114,8 @@ private:
   PDoubleVector fMarkerSizeList;
   PIntVector    fColorList;
 
+  bool fWithLines{false};
+
   virtual void CreateStyle();
   virtual void InitMuppCanvas(const Char_t* title, Int_t wtopx, Int_t wtopy, Int_t ww, Int_t wh);