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/imagecachingdialog.cpp

@@ -82,7 +82,7 @@ bool ImageCachingDialog::createCacheDirectory(QString dstPath)
 bool ImageCachingDialog::recursiveDelete(const QDir &dir)
 {
     QString abspath =  dir.absolutePath();
-    qDebug() <<abspath.toAscii();
+    qDebug() <<abspath.toLocal8Bit();
 
     //QList<QFileInfo> infLst = dir.entryInfoList(QStringList("*.jpg"), QDir::NoSymLinks);
     QStringList flist = dir.entryList(QStringList("*.jpg"), QDir::NoSymLinks | QDir::Files );