* 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