OpenVX C++ wrappers docs (#7681)

* adding wrapper headers to the project to see them in IDE project explorer

* readme

* doxygen: toplevel brief-s

* more doxygen

* more doxygen

https://github.com/opencv/opencv/issues/7590

happens on msys2 with gcc 6.2.0
see also http://stackoverflow.com/questions/38552221/undefined-reference-to-cvredirecterror-while-creating-shared-build-of-opencv-3

Change contour test images to be very wide (#7464)

* Change contour test images to be very wide (#7409, #7458)

Unfortunately, slows down the tests.

* Decrease the number of contour test cases, in order to (at least partially) offset the test run duration increase caused by making the test images wider

* Don't test with very wide images on 32-bit architectures

It improves 108%~230% performance in the perf test
with image format "CV_8UC1" and kernel size 3.
Signed-off-by: Li Peng <peng.li@intel.com>

/usr/lib/python3.5/re.py:203: FutureWarning: split() requires a non-empty pattern match.
  return _compile(pattern, flags).split(string, maxsplit)

C++ wrappers over OpenVX 1.x API (#7550)

* initial commit

* fixing missing swap(refcount) bug

* removing dead code

* fixinf identation

* splitting c++98 and external refcount definitions

* fixing formatToMatType

* using vector instead of initializer_list for consistency with c++98 API

* IVX_HIDE_INFO_WARNINGS

* just in case a compiler doesn't do this

* removing copy functionality from ImagePatch, Image can be used for that

* stricter type checks

iters should be 0 if we have no distortion. Also skip tilt distortion in
that case.
Furthermore move variable declarations to usage sites.