Fix calls to gnorb-trigger-todo-action

gnorb-trigger-todo-action requires the prefix arg from the calling
function. It doesn't actually do anything with it yet, but it wants it!

* lisp/gnorb-gnus.el (gnorb-gnus-incoming-do-todo): Pass in prefix arg.
* lisp/gnorb-org.el (gnorb-org-restore-after-send): Pass in nil prefix arg.
Restore action shouldn't quit summary buffer

Now that we have `gnorb-restore-layout', leave the summary buffer
intact, and switch to the appropriate Org file before triggering action.
This will also work better with triggering multiple relevant headings.

* lisp/gnorb-org.el (gnorb-org-restore-after-send): Don't mess with
  layout; explicitly switch to target Org buffer.