Refactoring carousel to not resize non-carousel embeddables

[#49877927]
See https://www.pivotaltracker.com/story/show/49883371 for the comment where this cropped up: the resizing was happening regardless of whether the carousel was actually needed, and in some cases it was setting the embeddable max-height to 0, which caused layout issues.
Separating questions from buttons [#49877927]

https://www.pivotaltracker.com/story/show/49877927
Don't resize if there's no carousel
Experiment with better error reporting for publish

[#51518791] - trying to put a better error message in the flash hash

https://www.pivotaltracker.com/story/show/51518791
A bit less in the cookie
Ensure we don't clobber our own flash
A bit more documentation of a failed publish
Putting more debugging data in the Rails log [#51518791]

https://www.pivotaltracker.com/story/show/51518791
Using the arrows icon for modal close [#49883371]

The inverse of the icon we use for opening the lightbox.

https://www.pivotaltracker.com/story/show/49883371
Get rid of the blue outline after closing colorbox

[#49883371]

https://www.pivotaltracker.com/story/show/49883371
Adding video scripts, hard-coded video tag
Merge branch 'refs/heads/master' into video-interactives