Changing email TODO handling to operate by org ID

gnorb-utils.el: new var gnorb-message-org-ids

Instead of marking mail TODOs as done based only on position of point in
a window configuration, we now stick the TODO's ID value into the
message as a custom header. When the mail is sent, the custom header is
stripped, and the user returned to the TODO with the matching ID. should
be a little more robust.
Moving the mail header stuff to a different file

It's better off in gnorb-utils than gnorb-gnus. Renaming the var to
gnorb-mail-header.
Comments on editing messages

I was considering editing received messages to add the Org ID header,
but it doesn't look like you can edit IMAP messages without major
destruction, so I'm probably going to drop this experiment. Everything
is commented out.
Rework Org BBDB popups

gnorb-org.el: Used to be Agenda-only, now works in both Agenda and
regular org files. Function `gnorb-org-agenda-popup-bbdb' renamed to
`gnorb-org-popup-bbdb'.
Wishlist item for outgoing messages

README:.org: Would like to create Org TODOs when sending a message, to
remind to check for response. Basically trigger the capture process on
message send.
Rework gnorb-org-restore-after-send

Now does a better job of ensuring that we're restored to the correct Org
heading. Also supports visiting multiple Org headings, though there's
currently no way to set up multiple headings.
Random comment edits and indenting changes.

gnorb-org.el