Feature: add dendrite to population display

We can add dendrites to the path, and they do appear in the population diagram, however, they create a loop. To prevent this, logic should be employed so that when entity = dendrite, it ONLY connects to Soma, and nothing else (i.e., other vias like axons).

To make it more understandable, changing the symbol for dendrite to a different shape would make it more understandable.
Perhaps a triangle?

When drawing the population display, dendrites should be placed at "top" of soma, same logic ordering as how axon sensory terminals are displayed.

see: https://composer.scicrunch.io/statement/23