Epi models: neighborhood highlighting should be 2-hops instead of one

[RosaRomeroGomez]

• Currently epi model variables always go through a function node so the highlighting is not that interesting.
• Modify or create a new neighborhood algorithm for this so it includes 2 hops instead of one.

[YohannParis]

So basically, the idea is that when the graph is expanded, we get node neighborhood highlighting on node selection. However, when the selected node is collapsed or it is connected to a collapsed node, the neighborhood highlighting breaks. I wouldn’t spend a lot of time on this task, if you see it is too complicated, we can just handle it in the demo