Merge pull request #2182 from LeonidBeynenson:lb/tracking_by_matching

* Add tracking-by_matching code and sample

* Make interface for PedestrianTracker

* Replace PedestrianTracker -> TrackerByMatching

* Make proper filtering by class id in tracking_by_matching

Also make the sample build in the case when opencv_dnn module is not
built.
Also help is added.

* Remove TODO-s from tracking_by_matching code

* Add parameter frame_step, add copyrights, fix warnings

* Remove copyright from tracking_by_matching

* Rename check macros and remove obsolete mentions of pedestrians

* Tune default thresholds in tracking_by_matching sample

* Add description of classes and factories

* Remove unrequired EOL-s at the end of files

* Replace pointers by references for output parameters

* Fix some warnings found by buildbot

* Fix warning from buildbot, tune some thresholds in tracking_by_matching

* Replace pragma once by ifndef-define clause

* Fix more Windows warnings

* Change case of methods of TrackerByMatching class

* Change name of methods to CamelCase in TrackerByMatching

* Make more convenient check macros in tracking_by_matching.cpp

* Simplify tracking_by_matching sample

* Fix Mac error in tracking_by_matching

Author: LeonidBeynenson