Refactor UserID Certificate details

The old code was obscurely optimized to avoid copying data
for the useridmodel. The userID model is fairly small as it
only works with the Signatures of the UIDs of a single key.
In most cases this is not much data. Keys with more then
a thousand signatures are rare and even those modern Systems
handle easily.

Reflecting this the option to specifically load certifications
is gone. Even for keys with lots of signatures liek
0xE3EDFAE3 or 0xD21739E9 this feels like instant. So no need
to hassle a user that explicitly selects UserID and Certification
details with yet another click to load them.

This also changes the UserIDListModel API to a Qt API.

BUG: 357933
REVIEW: 127059