When compiling with OpenNI2 flag active, CMake will not be able to find OpenNI.h due to the environment path not set in OpenCVFindOpenNI2.cmake. This PR rectifies this issue.

Fixed dynamic build script for iOS (#10923)

* Readded UIDeviceFamily (was removed in beec247)

* Added correct bitcode flag to python build script for iOS

* Missed the bitcodedisabled check

* Corrected the syntax in my proposed changes

  * add ifdef to apply on specific situation

* Fix #10948

* Add test code

* Fixed build error

* Add value zero

* eigen: test cleanup

Refactor decolor (#11035)

* decolor: modernize deprecated headers (math.h -> cmath)

* refactor contrast_preserve.cpp

* refactor contrast_preserve.hpp (add static/const)

* refactor contrast_preserve.hpp (join assignment and declaration)

* refactor contrast_preserve.hpp (format)

* refactor test_decolor.cpp (indent)

* refactor contrast_preserve.hpp (const)

* contrast_preserve.hpp : optimize by minMaxLoc

* fix trailing-whitespace

* fix warning C4267 on VC++ x64
(conversion from 'size_t' to 'int', possible loss of data)

* use cvRound instead of round_num

* decrease indentation of test_decolor.cpp

* remove pow() to optimize

* remove redundant Mat initialization

Enabling build of visualization module when using VTK 9 (current HEAD of d5bbb9e99bbc6d11d2196c48bfd8f33508554551)

Without proposed change, module throws build error regarding missing `opencv2/cudaimgproc.hpp`

This suppresses the interpretation of string literals by switching the ocv_download_log from a macro to a function.
This avoid crashes when the string to log contains escape characters.

More details about the problem this PR fixes are available at: https://github.com/opencv/opencv_contrib/issues/1131

* optimized cv::decolor by removing vector.push_back

* restored CV_INSTRUMENT_REGION() and original indent

* fix build warnings in contrast_preserve.hpp

* undo refactoring contrast_preserve.cpp/hpp

  * avoid misuse of vzeroupper on Visual Studio 2013 Update 5
  * add ifdef to avoid unattended optimization

- bgfg_segm
- peopledetect
- opencv_version
- dnn/colorization
- tapi/opencl_custom_kernel
- tapi/dense_optical_flow (renamed tvl1_optical_flow)

  * avoid aggressive optimization on Visual Studio 2012 Update 5
  * add code branch to avoid unattended optimization (keep the old code)

* SSE2 : use _mm_cvtpd_epi32 when converting from CV_64F to CV_32S

* No need to define a new universal intrinsic

* clean npr functions of useless initializations (speed-up)

* photo: remove unnecessary code