If no subkey is found (wrong fpr) or not provided, the expiry time of
the key is set instead.
setExpire() allows to expire all subkeys at once. Not implemented here.
Requires GPGME >= 1.15.0.
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).
A private key should be editable to Unknown or Ultimate levels only.
A public key should be editable to all levels except Ultimate.
Undefined level is excluded for both public and private keys.
The public WTreeTableNode may list private keys if the user does not manage
these private keys. Inform of this state in the tool tip. The certification
trust level is excluded for any change.
Imported primary keys also have unknown trust level, when they have
been generated in other keyrings.
Later, we should decide whether to exclude any primary key with ultimate
trust level from any further change.
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.
