* Fix several issues in TrackerMedianFlow implementation

Particularly, add possibility to tune optical flow parameters for a median
flow tracker.

* Improve code of TrackerMedianFlow

Replace a lot of calls of std::vector::erase by one call of
std::remove_if.

* Delete unused code, use norm from OpenCV

* medianFlow:turn getMedian method into function, small code cleanup

* TrackerMedianFlow:fixes in parameters I/O, add test for them

* TrackerMedianFlow:replace double with float in temp buffers

* Fix indentation

* TrackerMedianFlow:add absent parameter case handling in read()

* TrackerMedianFlow:use ROI instead of copy when getting a patch

* TrackerMedianFlow:don't calc image pyramids 2 times

* MedianFlowTracker: use cvIsNan()

* MedianFlow: refactor vector filtration code

* MedianFlow: change if statements layout in filterPointsInVectors