Upgraded Qwt to 6.2 (branch: qwt-multiaxes) (#4427)

This commit is based on https://github.com/GoldenCheetah/GoldenCheetah/pull/3956
with the following additions / changes:
* Upgraded to the latest version of the multiaxes-branch, thus eliminating crashes of GoldenCheetah on startup
* Disabled the emitting of Layout Requests on geometry changes of QwtScaleWidget - without this, CPU utilization was up to 100% on one core
* Added the class SplineLookup, reusing small portions of code from Qwt 6.1
* Re-added the splines in WPrime and RideFile (resampling), using the new interface of QwtSpline
* Appveyor: qwt in cache-section now depends on qwt/qwtconfig.prin.in for refresh on version change

qwt/examples/scatterplot/main.cpp

@@ -1,13 +1,53 @@
-#include <qapplication.h>
-#include "mainwindow.h"
+/*****************************************************************************
+ * Qwt Examples - Copyright (C) 2002 Uwe Rathmann
+ * This file may be used under the terms of the 3-clause BSD License
+ *****************************************************************************/
 
-int main( int argc, char **argv )
+#include "Plot.h"
+
+#include <QwtMath>
+#include <QApplication>
+
+static inline double randomValue()
 {
-    QApplication a( argc, argv );
-
-    MainWindow w;
-	w.resize( 800, 600 );
-    w.show();
-
-    return a.exec();
+    // a number between [ 0.0, 1.0 ]
+    return ( qwtRand() % 100000 ) / 100000.0;
+}
+
+class ScatterPlot : public Plot
+{
+  public:
+    ScatterPlot()
+    {
+        setTitle( "Scatter Plot" );
+
+        // a million points
+
+        const int numPoints = 100000;
+
+        QPolygonF samples;
+        samples.reserve( numPoints );
+
+        for ( int i = 0; i < numPoints; i++ )
+        {
+            const double x = randomValue() * 24.0 + 1.0;
+            const double y = std::log( 10.0 * ( x - 1.0 ) + 1.0 )
+                * ( randomValue() * 0.5 + 0.9 );
+
+            samples += QPointF( x, y );
+        }
+
+        setSamples( samples );
+    }
+};
+
+int main( int argc, char* argv[] )
+{
+    QApplication app( argc, argv );
+
+    ScatterPlot plot;
+    plot.resize( 800, 600 );
+    plot.show();
+
+    return app.exec();
 }