Reason:
Extrapolating from some issues and questions, users tend to want to delete old keys if they create a new one. And others requested a feature to disable certificates because they don't want them to clutter up their keyring.
We want to be able to tell users that they should keep their old keys (to decrypt old data) but don't have to see them if they mark them "disabled" and use this new filter instead of "All certificates"
Therefore this new filter should show all certificates/keys except the disabled ones.
The name is still up for discussion, another possibility: "All active certificates".
We could make this filter the default one, too.