implement RFE 3314, 'user can't see validity of gpg signatures' [SIC]

also a little reformatting of similar strings
update sf.net project link
better implementation of 420e8349978b7c927a80f1a5dd63fd737526feed. thanks to Ticho for the push.
Fix compat with libarchive 2.8.x (killed by 3.10.1-85-ga5e54ec).
Merge branch 'master' of ssh+git://git.claws-mail.org/home/git/claws