Modified sparse pyrlk optical flow to allow input of an image pyramid which thus allows caching of image pyramids on successive calls.
Added unsigned char support for 1, 3, 4 channel images.

fixes #5443

fixes #5643

fixes #5689

#5858 for master

fixes #5853 #4740

OpenCV 3.1.0

cap_v4l is better maintained and generally the code is in
better shape than cap_libv4l.