Updated qwt to 6.3 (qwt-multiaxes branch) (#4497)

Using qwt from https://sourceforge.net/p/qwt/git/ci/qwt-multiaxes/tree/

Applied the following changes to qwt 6.3:
* Added QwtZone to qwt_plot_curve.cpp
* Disabled the emitting of Layout Requests on geometry changes of
  QwtScaleWidget - without this, CPU utilization was up to 100% on
  one core

Fixes #4495

qwt/src/qwt_polar_panner.cpp

@@ -115,6 +115,4 @@ void QwtPolarPanner::widgetMousePressEvent( QMouseEvent* event )
     }
 }
 
-#if QWT_MOC_INCLUDE
 #include "moc_qwt_polar_panner.cpp"
-#endif