parsemail-mbox: Give a progress indication

Right now, parsemail-mbox doesn't give any progress information about
what it's doing and the whole process can take a long time with big
mailboxes.

Print the subject of the mail being parsed as the progress information.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
parsemail-mbox: Give a way to exclude Message-IDs from the parsing

Got a mbox archive with a 1MB mail among the mails and I really want to
way to skip this one.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
parsemail-mbox: Add a way to only parse a few selected message

We may only be interested a a few selected messages from the mbox file,
so provide a way to select those.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>