[feat] Add (Brief) Factor Description on "Population Density Chart"

[Sam-Runner]

On the "Population Density Chart", add a fly-out (on hover) or similar for the various factor breakdowns.

The intention here is that it can be hard to remember what all of the individual factors are, and what they actually mean. As such, having the ability to hover over a given Factor on the chart and see its name + the definition would be useful for persons reviewing the data, so they can be reminded of the significance of each Factor as they review it on the chart.