Support asymmetric padding in pooling layer (#12519)

* Add Inception_V1 support in ONNX

* Add asymmetric padding in OpenCL and Inference engine

* Refactoring

* feat: move gcgraph to detail

* chore: puts gcgraph cv::detail namespace

* matlab: move to opencv_contrib

* cmake: preserve variables scope for processing modules

- use macro instead of function to avoid scope resets

Minor changes in docs (Python Tutorials)

Correcting indentation of border type flags

For some mysterious (for me) reason, two lines of the code appears in my browser (Chrome) in the same line.
I've add an "enter" (just pressed enter), but don't know if it's the best solution.

* Fix perpendicular decision of RotatedRect::RotatedRect

Error estimation is based on #12455.

* Fix abs to std::fabs and atan to std::atan