* update the various places where the modest-window-mgr was used to register

* update the various places where the modest-window-mgr was used to register
  the header *before* the message is opened (see previous patch).
* also update the dimming rules, so opened messages will  have the delete
  button in the main window dimmed, as well, as when selecting multiple of
  which one or more are opened already.

pmo-trunk-r2492