Instead of "Quit" button, add a menu of actions
(make Quit indirect so you can't click it by accident).

Menu should include:
  go to First and Last slide.
  go to a particular slide.

Take a screenshot

Allow placement:

 0010L-hello.html   +-----------+-----------+
 0010R-hello.html   |           |           |
                    |     L     |     R     |
                    |           |           |
                    +-----------+-----------+

similarly 'A' (above) and 'B' (below).

Allow placement across monitors.

Allow talk notes to be placed permanently on one monitor (is this
useful though?  speaker could just open an editor with the notes
separately).

Fix Gtk2::Embed so it doesn't keep crashing and so we can
run everything in a single process.