Inner bg background positioning
Ui-selectable class is no longer removed from the transition editor

Need to go over and possibly re-factor all the background and surface
choosing code.  It started simple but got steadily more complicated and
convoluted as more capabilities were added such as:

1. Deck background
2. Per slide background
3. Deck surface
4. Per slide surface
5. Reset slide to deck background
6. Reset slide to deck surface
7. Custom bg image (per slide or deck)
8. Custom surface image (per slide or deck)
9. Handle old decks that are missing the surface attribute
10. Handle old decks that are missing the deck attribute
11. Preview the surface as user hovers their mouse over it
12. Preview the background
13. Apply the surface as the slide background for slides that are not
displayed on a surface
14. Apply a transparent background for the slide background for slides
that should be transparent

...