 touch activity when touch events occur
User activity is used to determine when controls should show/hide. It's
relatively simple when it comes to mouse events, because any mouse event
should show the controls. So we capture mouse events that bubble up to the
player and report activity when that happens.
With touch events it isn't as easy. We can't rely on touch events at the
player level, because a tap (touchstart + touchend) on the video itself on
mobile devices is meant to turn controls off (and on). Use