Add a people filter to only see folks with overdue rentals

[fpagnoux]

And / or: highlight overdue renters in the open rentals filter view.

[mprat]

One thing to add here: in the old UI under manage people -> open rentals, there was a button called "export emails" that means you could just bulk-send an email to everyone who had an open rental. When I was desk captain way back in the day this is how I did it. One thing to consider would be adding back this button.

See old issue reference: https://github.com/mitoc/gear-db-django/issues/91