Certified user identities in keys can be revoked using the same popup
for certification.
Requires GnuPG 2.2.24 (not available in distro's repository, not fully
tested to date).
In-place editing with a popup if user is allowed in app config file.
User must of course manage at least a private key. User identities of
target key may be selectively chosen. Optionally, certification may be
exportable and non-revocable.
