Channels exposure compensators (#13532)

* feed compatible with single channel images

* Simplified BlockGainCompensator::apply

* ChannelsCompensator

* BlocksChannelsCompensator

* Make source level compatibility detector happy

* dnn/Vulkan: fix GPU hang for heavy convolution tasks

Intel i915 driver will declare GPU hang if the compute shader
takes too long to complete. See
https://bugs.freedesktop.org/show_bug.cgi?id=108947 for details.

The idea in this commit is to divide heavy task into several light
ones and run compute shader multiple times to make each run take
short time enough.

TODO: Add more efficient compute shader
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

* dnn/Vulkan: add a more efficient conv shader

* Split videoio dependencies search into pieces, removed obsolete backends

Stitching: multi-feed on gain and block compensator (#13503)

* multi-feed on gain and block compensator

* ABI compatibility

Check for "gutter" around displayed image. there was one row/column missing on the bottom/right.
Might as well set gutter = 0?

* Fix drawMatches and drawKeypoints for BGRA input images

* keep BGRA too

* Combine different input types for drawMatches test

Added filter2d tests for 16S

OpenCV 4.0.1

OpenCV 4.0.1 for Intel(R) OpenVINO(TM) toolkit

Commit: 124011c3
PR: https://github.com/opencv/opencv/pull/13392

Sobel filter with 16S/16U datatype is broken.

OpenCV 3.4.5