schleuder should properly handle OpenPGP keys with raw e-mail addresses as the User ID

Given a key generated with:

gpg --batch --quick-gen-key 'alice@example.com'

Its user ID doesn't have any angle brackets in it.

If such an OpenPGP certificate gets imported to schleuder, schleuder does some weird things.

For one thing, it doesn't appear to associate that key with any e-mail address.

For another, when you do:

schleuder-cli list list@example.net

then the list duplicates the fingerprint in question on the first line of the output list. So before the import it shows:

6789012345678901234567890123456789012345 subscriber1@example.org
1234567890123456789012345678901234567890 subscriber2@example.biz

and after it shows:

3456789012345678901234567890123456789012 6789012345678901234567890123456789012345 subscriber1@example.org
1234567890123456789012345678901234567890 subscriber2@example.biz

yikes!

These kinds of User IDs are not wide-spread. Autocrypt recommends using <foo@example.org> instead of foo@example.org and schleuder#146 also suggests wrapping addresses in angle brackets (<>). But some user IDs like that do exist in the wild, and schleuder should handle them more gracefully.