Rename gnorb-org-window-conf to gnorb-window-conf

Should be saved as a more central value.

* lisp/gnorb-utils.el: Add gnorb-window-conf, and use new var
* lisp/gnorb-org.el: Remove gnorb-org-window-conf
* lisp/gnorb-gnus.el: Use new var
Use a marker in conjunction with window conf

We use gnorb-window-conf for returning from various actions. You're
not supposed to rely on that for position of point, so pair it with a
marker for finding point.

* lisp/gnorb-utils.el (gnorb-return-marker): New variable pointing at
  marker
* lisp/gnorb-gnus.el: Use it
* lisp/gnorb-org.el: Use it
Don't force id creation!

* lisp/gnorb-org.el (gnorb-org-view): Was calling org-id-get-create with
  the force argument, I have no idea why, which was screwing up tracking.