p5js/mitosis - Add draft of Cytokinesis
p5js/mitosis - Add draft of Cytokinesis

* At the start of Cytokinesis, pick one of the Membrane segment points, and the one opposite it.
* Mark them as 'FurrowPoints'  (borrowing language from the term Cleavage Furrow which describes how the pinching of the cell membrane).
  - this will stop their normal vibration
  - throughout the Cytokinesis phase, slowly move them towards each other

There are couple of broken aspects:
1. After Cytokinesis, these points should be marked as no longer being FurrowPoints (so they can vibrate)
2. After Cytokinesis, we should really form a new Cell object, and give other Cell half of the membrane.

brianhonohan/sketchbook,brianhonohan/sketchbook,brianhonohan/sketchbook