Figure out what the `ent_pop_id` is on a Historical Figure

[bbenefield89]

This issue is open for anyone willing to take it.

Most, if not all, Historical Figures have a property ent_pop_id that contains a number. I'm not exactly sure what this number represents.

• Figure out what ent_pop_id is
• Decide if it should be displayed
• If important, how can we use it?