Utility method for representing BoundingBox in cv2 style.  Accept parameter to the BoundingBox.update method in either of these formats.
Reworked CamshiftTracker.  Uses HSVColourSegmenter to find the mask for finding the histogram.  The tracker will now track objects that have already been found through some other method, updating their location at each frame.
Reworked ShapeFeatureTracker to essentially find objects of interest, then hand them off to the CamshiftTracker once it is fairly sure they are legitimate objects.  This required introducing the notion of potential objects and known objects in the ShapeFeatureTracker.  The MultistageTracker class mediates the handoff, and is the class that gets used in the analyzer.  The application's fish count is determined based on the number of objects handed off.