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>

modules/features2d/test/test_keypoints.cpp

@@ -40,7 +40,7 @@
 //M*/
 
 #include "test_precomp.hpp"
-#include "opencv2/highgui/highgui.hpp"
+#include "opencv2/highgui.hpp"
 
 using namespace std;
 using namespace cv;