Set headers for no auto response on most emails

Set headers for no auto response on most emails

Most of our auto-generated emails should not ask for auto replies (like
out of office messages or in particular, "held for moderation" notices
from our own list server), so set this header by default, and also the
header indicating if it's an auto submitted/auto replied message.

Specifically allow auto replies on moderation notices, since that's a
case where it might be really interesting for the moderator to see for
example an out of office message. At least for now that seems like a
good idea.