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

...
Two UI niceties for the slide well

*Adds padding to the bottom* so the "Add Slide" button is easily accessible on mouseover when the slide being appended to is at the very bottom of the list (removes the need to scroll further to access it & generally makes it easier/nicer to use).

*Adds a z-index* so slide content doesn't obstruct the slide well. Went with the same z-index that's already being used for the navbar (figured the navbar & slide well are equally important).
Increase z-index to coincide with slide well adding z-index

https://github.com/tantaman/Strut/pull/220 shows a need to add a z-index to the slide well, but this means the navbar-inner z-index needs to be increased so the dropdown isn't covered up.
More consistent naming for background and surface classes
Changed defaultbg to bg-default
Changed transparentbg to bg-transparent
Changed imgbg to bg-img
Made swap bg take advantage of the standardized bg class names
Moved background class manipulation code into a centralized location
Updated presentation generators to conform to the consistent background
naming
Created a specific template for the surface chooser

transparency doesn't make sense for the surface.
Fixed the class editor

Stops prop on mousedown to prevent the jquery ui selectable from firing
Merge branch 'production'
Merge remote-tracking branch 'kzeni/patch-2' into kzeni-test
Merge remote-tracking branch 'kzeni/patch-3' into kzeni-test
Check for the existence of the bg parameter before using it
Fixed the class editor from losing its event bindings on switching modes
Closes the bootstrap dropdown on selectablestart
Don't apply bg img as a bg class