Add GpgOL and Gpgtools mime filenames to classify

GpgOL from the next version on will use .mime as a file extension
for its internal attachment, which is only visible if it has
not been converted to MIME from MAPI. This also adds Gpgtools
(AppleMail) PGP attachment filename.

(cherry picked from commit cb4217632f1c5bc0e09c65968837ae7432979771)