Support asymmetric padding in pooling layer (#12519)

* Add Inception_V1 support in ONNX

* Add asymmetric padding in OpenCL and Inference engine

* Refactoring

* 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

When cross compiling with clang, the internal C++ headers are not found
when adding sysroot to -isystem, that is redundant anyway because it
will look for headers insider --sysroot path with same quality as it
would do with -isystem otherwise

Fixes errors like

FAILED: 3rdparty/openexr/CMakeFiles/IlmImf.dir/Iex/IexBaseExc.cpp.o
....
In file included from
TOPDIR/build/tmp/work/cortexa7t2hf-neon-vfpv4-bec-linux-musleabi/opencv/3.4.3+gitAUTOINC+b38c50b3_1f6d6f0626_bdb7bb85f3_34e4206aef_fccf7cd6a4-r0/git/3rdparty/openexr/Iex/IexBaseExc.cpp:43:
In file included from
TOPDIR/build/tmp/work/cortexa7t2hf-neon-vfpv4-bec-linux-musleabi/opencv/3.4.3+gitAUTOINC+b38c50b3_1f6d6f0626_bdb7bb85f3_34e4206aef_fccf7cd6a4-r0/git/3rdparty/openexr/Iex/IexBaseExc.h:48:
In file included from
TOPDIR/build/tmp/work/cortexa7t2hf-neon-vfpv4-bec-linux-musleabi/opencv/3.4.3+gitAUTOINC+b38c50b3_1f6d6f0626_bdb7bb85f3_34e4206aef_fccf7cd6a4-r0/recipe-sysroot/usr/lib//arm-bec-linux-musleabi/8.2.0/../../../include/c++/8.2.0/string:52:
In file included from
TOPDIR/build/tmp/work/cortexa7t2hf-neon-vfpv4-bec-linux-musleabi/opencv/3.4.3+gitAUTOINC+b38c50b3_1f6d6f0626_bdb7bb85f3_34e4206aef_fccf7cd6a4-r0/recipe-sysroot/usr/lib//arm-bec-linux-musleabi/8.2.0/../../../include/c++/8.2.0/bits/basic_string.h:6391:
In file included from
TOPDIR/build/tmp/work/cortexa7t2hf-neon-vfpv4-bec-linux-musleabi/opencv/3.4.3+gitAUTOINC+b38c50b3_1f6d6f0626_bdb7bb85f3_34e4206aef_fccf7cd6a4-r0/recipe-sysroot/usr/lib//arm-bec-linux-musleabi/8.2.0/../../../include/c++/8.2.0/ext/string_conversions.h:41:
TOPDIR/build/tmp/work/cortexa7t2hf-neon-vfpv4-bec-linux-musleabi/opencv/3.4.3+gitAUTOINC+b38c50b3_1f6d6f0626_bdb7bb85f3_34e4206aef_fccf7cd6a4-r0/recipe-sysroot/usr/lib//arm-bec-linux-musleabi/8.2.0/../../../include/c++/8.2.0/cstdlib:75:15:
fatal error: 'stdlib.h' file not found
              ^~~~~~~~~~
1 error generated.
Signed-off-by: Khem Raj <raj.khem@gmail.com>