Revert "Fix Markdown nested inside HTML"

This reverts commit d9bb138970389e1b33b47789b0e8d4c3e40bc23a.
Fix markup for Video Production tutorial.

Looks like this was another bug caused by the switch to kramdown. The
inner divs now all need to set markdown="1", and kramdown appears to be
more strict with whitespace.

Note: The blank lines after the images are required for the captions to
be rendered properly.