Add functionality to save inference images for the debugging purposes.

Save bmp images of inference results to /tmp as bmp files. BMP was
chosen to reduce encoding time. Saving is fully threaded. It can be
enable with qmake CONFIG+=save_images option

Also:
  - use antialised fonts in RKNN inference
  - moved class strings to inference base class
  - fixed silly segfault in ONNX inference
  - prevent writing results if class if exceeds valid values

Issue: https://denyspopov.atlassian.net/browse/AZ-38
Type: Improvement

misc/rtsp_ai_player/aiengineimagesaver.cpp

@@ -0,0 +1,31 @@
+#include <QFile>
+#include <QDataStream>
+#include <QDebug>
+#include "aiengineimagesaver.h"
+
+AiEngineImageSaver::AiEngineImageSaver(const cv::Mat &image, int imageNumber, QObject *parent)
+    : QThread(parent), image(image.clone()), imageNumber(imageNumber)
+{
+}
+
+AiEngineImageSaver::~AiEngineImageSaver()
+{
+    wait();
+}
+
+void AiEngineImageSaver::run()
+{
+    if (image.empty() || image.channels() == 0) {
+        qWarning() << "AiEngineImageSaver. Empty image or no channels, nothing to save.";
+        return;
+    }
+
+    // Calculate the size of the upper half
+    int halfHeight = image.rows / 2;
+    cv::Mat upperHalf = image(cv::Rect(0, 0, image.cols, halfHeight));
+
+    // Use bpm to reduce encoding time.
+    QString filePath = QString("/tmp/image-%1.bmp").arg(imageNumber, 5, 10, QChar('0'));
+
+    cv::imwrite(filePath.toStdString(), upperHalf);
+}