Restore from mails more reliably

* gnorb-gnus.el: gnorb-gnus-check-org-header

gnorb-org-setup-message adds the restore function to
message-exit-actions, but in case we're working from a saved draft or
buffer-local vars have otherwise been wiped, we add the restore
function here as well.
That's not broken anymore.
Whoops.
First whack at gnorb-gnus-message-trigger-todo

* gnorb-gnus.el: new function

This works fine as it is, but it's not that exciting yet.
Various docstring and comment edits.

Hopefully nothing important.
New generalized function gnorb-trigger-todo-action

lisp/gnorb-gnus.el: Renamed `gnorb-gnus-message-trigger-default' and
moved to gnorb-utils.el, now called `gnorb-trigger-todo-default'.

lisp/gnorb-utils.el: New function `gnorb-trigger-todo-action', new
variable `gnorb-gnus-trigger-refile-args'.

lisp/gnorb-org.el: Rework `gnorb-org-restore-after-send' to use
gnorb-trigger-todo-action

Basically, what happened is, as I was writing the gnorb-gnus TODO
triggering stuff, it seemed like we wanted just one triggering
routine (with its own options, etc), that both gnorb-gnus triggering and
gnorb-org handle email restore would use when visiting their respective
TODO headings.
Make TODOs from outgoing messages

lisp/gnorb-gnus.el: New function gnorb-gnus-outgoing-make-todo, and its
helper function gnorb-gnus-outgoing-make-todo-1. Renamed
`gnorb-gnus-check-org-header' to 'gnorb-gnus-check-outgoing-headers' to
reflect its more general purpose. New defvar
`gnorb-gnus-sending-message-info' where outgoing message information is
stored. New user option `gnorb-gnus-new-todo-capture-key' to specify
which capture template to use for outgoing messages.

lisp/gnorb-org.el: New user option `gnorb-org-msg-id-key', specifying
the name of the property where message ids are stored.

README.org: Document the above.
Split 'gnorb-org-email-subtree-parameters'

lisp/gnorb-org.el: `gnorb-org-email-subtree-parameters' is now split
into `gnorb-org-email-subtree-text-parameters' and
`gnorb-org-email-subtree-file-parameters'
Improve scanning of headings for mail actions

lisp/gnorb-org.el: New functions and options! The entry point,
		   `gnorb-org-extract-mail-stuff', has been tweaked to
		   call new function `gnorb-org-scan-state-notes' to see
		   if we should be replying to a message link in the
		   state notes. New option
		   `gnorb-org-mail-scan-state-changes' controls how that
		   works.

		   Another new option `gnorb-org-mail-scan-scope'
		   controls how much of the subtree is scanned for
		   links.

		   New option `gnorb-org-mail-scan-function', which
		   defaults to `gnorb-org-extract-mail-stuff', can be
		   set to a custom option.
New hook gnorb-org-after-message-setup-hook

lisp/gnorb-org.el: New hook `gnorb-org-after-message-setup-hook', run as
the last step message setup when composing/replying using
gnorb-org-setup-message.