Tracking-Learning-Detection and MedianFlow

This contribution includes the following logical components into
tracking module:

*) Change Rect to Rect2d into headers for Tracker's methods;
This contribution includes the following logical components into
tracking module:

*) Change Rect to Rect2d into headers for Tracker's methods;
*) MedianFlow tracker;
*) extensible benchmark to compare trackers interactively and
assess
them quantitatively;
*) TLD tracker (work-in-progress);

Work was funded by Google Summer of Code 2014 initiative. Mentors:
Gary
Bradski and Vadim Pisarevsky.
sometimes because of rounding errors you may get negative results before getting square root. You should use std::sqrt(std::max(..., 0.));