Report unparsed user ids during upload
A user was confused when the key that they uploaded had no parsable user ids (see also sequoia-pgp/sequoia#298 (closed)), and they got no info about that fact.
This MR adds a paragraph to the upload dialog that informs about the number of unparsed uids. It also links to a new FAQ entry with a slightly more elaborate description.
While I was at it, I also added and linked a FAQ entry about revoked identities.