Fix jarring update GenericChart with multiple plots

.. setUpdatesEnabled() to stop output did not help at
   all with respect to the jarring effet of watching
   plots added when in stack mode.

.. for some reason adding this QApplication::processEvents()
   fixes that. Go figure.

src/Charts/GenericChart.cpp

@@ -248,6 +248,13 @@ GenericChart::finaliseChart()
         }
     }
 
+    // update plot to stop the jarring effect as chart
+    // is updated, especially when multiple series in
+    // stack mode. I would expect this to make things
+    // worse but for some reason, it solves the problem.
+    // do not remove !!!
+    QApplication::processEvents();
+
     // now initialise all the newPlots
     for(int i=0; i<newPlots.count(); i++) {