Fixed compilation warnings in samples:

- use per-module includes instead of "opencv.hpp"
- unused function warnings
- undefined macro warning

samples/cpp/application_trace.cpp

@@ -1,7 +1,9 @@
 /* OpenCV Application Tracing support demo. */
 #include <iostream>
 
-#include <opencv2/opencv.hpp>
+#include <opencv2/core.hpp>
+#include <opencv2/imgproc.hpp>
+#include <opencv2/highgui.hpp>
 #include <opencv2/core/utils/trace.hpp>
 
 using namespace cv;