utility function: cloneObject
default video display style: "block"
for debugging: checkWaltzPoints();
preload next video, movement or interview
fix locationsForWaltz() bug

Waltz 4 and 29 both have movements at location 11.

But ... this location was missing when queried for 29:

  locationsForWaltz(4).length => 3
  locationsForWaltz(29).length => 2
fix alternation when multiple movement at location
smoother transitions between videos segments