Clone container contents instead of container itself

When the line wrap.html(container.html()); was changed to
wrap.html(container.clone(true)); it fixed the problem of JS events
getting lost, but now instead of copying the container content it makes
a duplicate of the container itself. This duplication leads to problems
with the default videoBG usage actually creating another body element
within the main body element, which in turn causes incompatibilities
with other plugins and code that perform operations on the “body”
element.

This commit still uses the jQuery clone() method to maintain JS events,
but instead of cloning the container, it clones the container’s
children (i.e. its content) into the videoBG wrapper.