Delete nms and tracker

[alpha-carinae29]

This will delete some of post processing steps since they are irrelevant duo to adding high accuracy pedestrian detectors.

[JsonSadler]

What was the harm? :D
I think keeping them is beneficial as some one may needed to use simpler/weaker detectors on less powerful platforms.
Instead, we can add a configuration flag for enable/disable it.
What do you think? @mhejrati

[mrn-mln]

@alpha-carinae29 I've implemented a new tracker and remove the centroid tracker class.