Major port Qt4 to Qt6

- Updated header inclusions from QtGui to QtWidgets for consistency and compatibility with Qt 5 and later.
- Replaced deprecated QApplication::desktop() with QApplication::primaryScreen() for obtaining screen DPI.
- Modified MyOutputHandler to use QMessageLogContext and QString for improved logging.
- Changed QMatrix to QTransform for image rotation in ImageCutout class.
- Updated various debug statements to use toLocal8Bit() instead of toAscii() for better string handling.
- Refactored several classes to use QElapsedTimer instead of QTime for performance measurement.
- Ensured all operator overloads in Section and Tag classes are marked as const for better const-correctness.

ClippingStation/main.cpp

@@ -17,7 +17,7 @@
  *
  ************************************************************************/
 
-#include <QtGui/QApplication>
+#include <QApplication>
 #include <QPluginLoader>
 
 #include "globalfunctions.h"
@@ -25,11 +25,10 @@
 
 int main(int argc, char *argv[])
 {
-    QApplication::setGraphicsSystem("raster");
     QApplication a(argc, argv);
 
     //g_logfile.open("clippingstation.log", ios::app);
-    qInstallMsgHandler(MyOutputHandler);
+    qInstallMessageHandler(MyOutputHandler);
 
     ClippingStation w;