Remove unnecessary and faulty new_frame detection.

This would only detect a non-new-frame when the camera input equalled
the filtered output, which would only happen after a long period of no
movement or noise. It also is not recommended for this type of filter.
Simplify first_run handling to only initialize filter states.
Make reset() set first_run=true;
Update filter constants for dt=3ms as used in tracker.cpp.

Change expressions and comments to make it easy to change dt.
Change noise filtering from 2mins to 60secs.
Rename alpha/smoothing/output vars/attrs with better names.
Simplify EWMA2 licence and add filter description comment.
Merge pull request #83 from dbaarda/dev/ewma2

Dev/ewma2