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/aiengine.cpp

@@ -2,6 +2,7 @@
 #include <opencv2/highgui.hpp>
 #include "aiengine.h"
 #include "aiengineinference.h"
+#include "aiengineimagesaver.h"
 
 #if defined(OPI5_BUILD)
 #include "src-opi5/aiengineinferenceopi5.h"
@@ -82,6 +83,13 @@ void AiEngine::inferenceResultsReceivedSlot(AiEngineInferenceResult result)
     }
 
     cv::imshow("Received Frame", result.frame);
+
+#ifdef SAVE_IMAGES
+    static int imageCounter = 0;
+    AiEngineImageSaver *saver = new AiEngineImageSaver(result.frame, ++imageCounter);
+    saver->start();
+    connect(saver, &AiEngineImageSaver::finished, saver, &QObject::deleteLater);
+#endif
 }