Filter option for including only biological relatives

[Mattkmmr]

@GeorgeWilmes

From the user perspective, it would be very simple: just a checkbox. But I imagine it would impact many places deep in the code. When selecting parents (or children) of a person, it would need to check for the “birth” relationship (child reference type?).

I’ll look into them. I’ve already added the same steps to my latest filter rules.