* tensorflow support mirror pad

* revert macro define

* revert macro define

* reduce code duplication

* revert macro define

* Support Eltwise3d

* Refactoring

* Fix test

Removed constants from legacy C api and switched out header with shorter version.

Removed blank line that was failing CI.

from MSVS2017 and GCC8 -O1 mode

misused 'optional' mode

- exception safe smart pointers, fixed many memory leaks
- fixed errors handling
- fixed strings handling
- fixed file existence check
- fixed toFraction() implementation
- add 'drop=true' for v4l2 input
- avoid overriding custom pipelines sink's 'max-buffers' value
- updated valgrind supression rules
- added support for GStreamer native leaks tracking (via gst_deinit() call)
- repaired capturing through GStreamer0.10 (fixed CV_8UC1)

causes leaks if FFmpeg is disabled through OPENCV_VIDEOIO_PRIORITY_FFMPEG=0

Test request by #14583 (#14800)

* add test to show the undistort bug

* move test to calib3d

* Remove Inference Engine 2018R3 and 2018R4

* Fix 2018R5

Fix for MSVS2019 build warnings (#14743)

* AVX512 arch support for MSVS

* Fix for MSVS2019 build warnings: updated integral() AVX512 implementation

* Fix for MSVS2019 build warnings: reworked v_rotate_right AVX512 implementation

* fix indentation

backporting of commit: d3d13c41

backporting of commit: f6230ae0

- use compile-time checks instead (`#if CV_SIMD128`)
- runtime checks are useless

* Support Slice layer in ONNX importer

* Add IE support

* Fix ONNX importer

* Fix Slice

* java: fix java SimpleBlobDetector

* add SIMPLEBLOBFeatureDetectorTest

* add package org.opencv.test.features2d;

* fix SIMPLEBLOBFeatureDetectorTest

backporting of commit: 76fca0e7

* Add Axpy layer

* Fix test

* fix caffe importer

Fix build issue on QNX platform (#14678)

* QNX compatibility

* core: unify gettimeofday() usage