OpenCV 3.4.6

- estimateAffine2D/estimateAffinePartial2D() calls

oss-fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13280
oss-fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13283

- replace tutorial links via docs.opencv.org
- remove link on OpenCV 2.4
- avoid links on outdated packages

* improve thresholding tutorial, fix grammar issues and incorrections

* keep full list of simple thresholding types

* Mac support for op inference engine

Adding condition to check for mac and add corresponding libraries

* Adding mac support in test cases

- more checks
- drop separate branches for 32FC1/32FC3(read) handling
- added for 32F/64F non-compressed
- added tests for 32FC3 (RAW + hdr SGILOG compression)
- added test 64FC1
- dump tiff errors on stderr

* Postpone variable definitions

* dnn: reduce scope of 'Mat image' variable

- models are moved out from OpenVINO package
- need to download them separatelly

backporting of commit: f2803aba

- use relative paths for includes
- fix PCH generation with GCC (dummy file has been used)

backporting of commit: 45428b89