gpgme-subkey / types: Add CAN_CERTIFY and CAN_AUTHENTICATE flags for PGP subkeys

We only supported CAN_ENCRYPT and CAN_SIGN, but subkeys can have these other two flags as well.

https://bugzilla.gnome.org/show_bug.cgi?id=733920
Signed-off-by: Federico Mena Quintero <federico@gnome.org>
pgp-subkey: Generate 'Certify' and 'Authenticate' names for the new flags

https://bugzilla.gnome.org/show_bug.cgi?id=733920
Signed-off-by: Federico Mena Quintero <federico@gnome.org>
Signed-off-by: Stef Walter <stefw@gnome.org>
 * Whitespace, make struct definition local