Main module headers are moved 1 level up

e.g. <opencv2/core/core.hpp> become <opencv2/core.hpp>

Also renamed <opencv2/core/opengl_interop.hpp> to <opencv2/core/opengl.hpp>

samples/cpp/stitching.cpp

@@ -42,8 +42,8 @@
 
 #include <iostream>
 #include <fstream>
-#include "opencv2/highgui/highgui.hpp"
-#include "opencv2/stitching/stitcher.hpp"
+#include "opencv2/highgui.hpp"
+#include "opencv2/stitching.hpp"
 
 using namespace std;
 using namespace cv;