improve global brightness classification heuristics
improve global brightness classification heuristics

Add hysteresis for light_bases detection. Revise current top of stack
on slow-rising signal across a few frames where the old code got confused
and treated the transient interpolated level as a new plateau.

informatics-isi-edu/fishspy,informatics-isi-edu/fishspy,informatics-isi-edu/fishspy,informatics-isi-edu/fishspy