Use ROI selector in python samples

- made some of dependencies explicit
- removed dependencies to highgui and some other modules where possible
- modified some samples to build without modules

* 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

For some applications it is useful to have an estimate of how uncertain
the specific variable is estimated. This could help to act accordingly
e.g. increase the measurement zone if the current estimate is very
uncertain. 

1. Multi-tracker classes (multiTracker.cpp)
2. Multi-tracker example (multiTracker_test.cpp)
3. Fixed a rare bug (OpenCL runtime error)

http://www.votchallenge.net/vot2015/dataset.html

1. Multi-tracker classes (multiTracker.cpp)
2. Multi-tracker example (multiTracker_test.cpp)
3. Fixed a rare bug (OpenCL runtime error)

http://www.votchallenge.net/vot2015/dataset.html

1. Multi-tracker classes (multiTracker.cpp)
2. Multi-tracker example (multiTracker_test.cpp)
3. Fixed a rare bug (OpenCL runtime error)

http://www.votchallenge.net/vot2015/dataset.html