allow filmstrip nav without filmstrip

This allows a user to keep show_filmstrip_nav=true even when setting show_filmstrip=false, thereby keeping the navigation buttons (play, pause, next, previous) visible on top of the image panel even if the filmstrip is hidden. Otherwise, there are no play/pause buttons to control the animation.

John Maurer <jmaurer@hawaii.edu>
Pacific Islands Ocean Observing System (PacIOOS)
University of Hawaii at Manoa