Spurious hello/goodby events when no motion in frame

[jschrempp]

When the field of view is unchanging, the Eyes will still occasionally emit an TOF event for someone entering the field of view. We've seen that there are spurious readings in any given cell. We've tried to filter that out by requiring several adjoining cells to go active at the same time, our theory is that rarely will a real human in the FOV register in just one cell.

The idea is to add some temporal filtering to the code so that an even is only triggered if something in the FOV remains there for some short period of time.