Draw fitted ellipses in diagnostic images

[ethanjli]

This PR adds functionality to draw the region's fitted ellipse in the tagged.jpg diagnostic images saved by the segmenter; those ellipses are useful for understanding biases in the ellipsoid biovolume estimates described at https://www.protocols.io/view/planktoscope-protocol-for-plankton-imaging-bp2l6bq3zgqe/v3?step=16 , and for comparing ellipsoid biovolume against plain/riddled biovolume estimates.

[ethanjli]

Here's a visual example of the change made by the above commits.
Before the commits:

After the commits:

[ethanjli]

The above commit adds drawings of two semicircles for each object in the diagnostic images: the upper semicircle corresponds to the circle with area equal to the object's filled area, while the lower semicircle corresponds to the circle with area equal to the object's area-excluding-holes. For example: