Median flow tracker update (#952)

* 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

modules/tracking/include/opencv2/tracking/tracker.hpp

@@ -1156,9 +1156,16 @@ class CV_EXPORTS TrackerMedianFlow : public Tracker
  public:
   struct CV_EXPORTS Params
   {
-    Params();
-    int pointsInGrid; //!<square root of number of keypoints used; increase it to trade
-                      //!<accurateness for speed; default value is sensible and recommended
+    Params(); //!<default constructor
+              //!<note that the default values of parameters are recommended for most of use cases
+    int pointsInGrid;      //!<square root of number of keypoints used; increase it to trade
+                           //!<accurateness for speed
+    cv::Size winSize;      //!<window size parameter for Lucas-Kanade optical flow
+    int maxLevel;          //!<maximal pyramid level number for Lucas-Kanade optical flow
+    TermCriteria termCriteria; //!<termination criteria for Lucas-Kanade optical flow
+    cv::Size winSizeNCC;   //!<window size around a point for normalized cross-correlation check
+    double maxMedianLengthOfDisplacementDifference; //!<criterion for loosing the tracked object
+
     void read( const FileNode& /*fn*/ );
     void write( FileStorage& /*fs*/ ) const;
   };