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/imagecachingthread.cpp

@@ -51,7 +51,7 @@ void ImageCachingThread::run()
         while( !m_imageCacheDlg.m_resume )
             return;
 
-        //qDebug() << "Copying " << m_srcFiles[i].toAscii();
+        //qDebug() << "Copying " << m_srcFiles[i].toLocal8Bit();
 
         if (m_imageCacheDlg.m_cachedImages[ m_dstPath+m_dstFiles[i] ] )
         {
@@ -92,7 +92,7 @@ bool ImageCachingThread::cacheFromFtpServer(QString srcPage, QString dstPage)
 
     char strerror[256];
 
-    bool ret = download(curlhandle, srcPage.toAscii(), dstPage.toAscii(), 0, 1, strerror);
+    bool ret = download(curlhandle, srcPage.toLocal8Bit(), dstPage.toLocal8Bit(), 0, 1, strerror);
 
     curl_easy_cleanup(curlhandle);
     curl_global_cleanup();