Merge pull request #13030 from dmatveev:tutorial

* G-API: First steps with tutorial

* G-API Tutorial: First iteration

* G-API port of anisotropic image segmentation tutorial;
* Currently works via OpenCV only;
* Some new kernels have been required.

* G-API Tutorial: added chapters on execution code, inspection, and profiling

* G-API Tutorial: make Fluid kernel headers public

For some reason, these headers were not moved to the public
headers subtree during the initial development. Somehow it even
worked for the existing workloads.

* G-API Tutorial: Fix a couple of issues found during the work

* Introduced Phase & Sqrt kernels, OCV & Fluid versions
* Extended GKernelPackage to allow kernel removal & policies on include()

All the above stuff needs to be tested, tests will be added later

* G-API Tutorial: added chapter on running Fluid backend

* G-API Tutorial: fix a number of issues in the text

* G-API Tutorial - some final updates

- Fixed post-merge issues after Sobel kernel renaming;
- Simplified G-API code a little bit;
- Put a conclusion note in text.

* G-API Tutorial - fix build issues in test/perf targets

Public headers were refactored but tests suites were not updated in time

* G-API Tutorial: Added tests & reference docs on new kernels

* Phase
* Sqrt

* G-API Tutorial: added link to the tutorial from the main module doc

* G-API Tutorial: Added tests on new GKernelPackage functionality

* G-API Tutorial: Extended InRange tests to cover 32F

* G-API Tutorial: Misc fixes

* Avoid building examples when gapi module is not there
* Added a volatile API disclaimer to G-API root documentation page

* G-API Tutorial: Fix perf tests build issue

This change came from master where Fluid kernels are still used
incorrectly.

* G-API Tutorial: Fixed channels support in Sqrt/Phase fluid kernels

Extended tests to cover this case

* G-API Tutorial: Fix text problems found on team review

samples/cpp/tutorial_code/ImgProc/anisotropic_image_segmentation/anisotropic_image_segmentation.cpp

@@ -10,7 +10,9 @@
 using namespace cv;
 using namespace std;
 
+//! [calcGST_proto]
 void calcGST(const Mat& inputImg, Mat& imgCoherencyOut, Mat& imgOrientationOut, int w);
+//! [calcGST_proto]
 
 int main()
 {
@@ -26,6 +28,7 @@ int main()
         return -1;
     }
 
+    //! [main_extra]
     //! [main]
     Mat imgCoherency, imgOrientation;
     calcGST(imgIn, imgCoherency, imgOrientation, W);
@@ -45,32 +48,36 @@ int main()
 
     normalize(imgCoherency, imgCoherency, 0, 255, NORM_MINMAX);
     normalize(imgOrientation, imgOrientation, 0, 255, NORM_MINMAX);
+
     imwrite("result.jpg", 0.5*(imgIn + imgBin));
     imwrite("Coherency.jpg", imgCoherency);
     imwrite("Orientation.jpg", imgOrientation);
+    //! [main_extra]
     return 0;
 }
 //! [calcGST]
+//! [calcJ_header]
 void calcGST(const Mat& inputImg, Mat& imgCoherencyOut, Mat& imgOrientationOut, int w)
 {
     Mat img;
-    inputImg.convertTo(img, CV_64F);
+    inputImg.convertTo(img, CV_32F);
 
     // GST components calculation (start)
     // J =  (J11 J12; J12 J22) - GST
     Mat imgDiffX, imgDiffY, imgDiffXY;
-    Sobel(img, imgDiffX, CV_64F, 1, 0, 3);
-    Sobel(img, imgDiffY, CV_64F, 0, 1, 3);
+    Sobel(img, imgDiffX, CV_32F, 1, 0, 3);
+    Sobel(img, imgDiffY, CV_32F, 0, 1, 3);
     multiply(imgDiffX, imgDiffY, imgDiffXY);
+    //! [calcJ_header]
 
     Mat imgDiffXX, imgDiffYY;
     multiply(imgDiffX, imgDiffX, imgDiffXX);
     multiply(imgDiffY, imgDiffY, imgDiffYY);
 
     Mat J11, J22, J12;      // J11, J22 and J12 are GST components
-    boxFilter(imgDiffXX, J11, CV_64F, Size(w, w));
-    boxFilter(imgDiffYY, J22, CV_64F, Size(w, w));
-    boxFilter(imgDiffXY, J12, CV_64F, Size(w, w));
+    boxFilter(imgDiffXX, J11, CV_32F, Size(w, w));
+    boxFilter(imgDiffYY, J22, CV_32F, Size(w, w));
+    boxFilter(imgDiffXY, J12, CV_32F, Size(w, w));
     // GST components calculation (stop)
 
     // eigenvalue calculation (start)