Bug#894414: pdf-presenter-console: cursor changesto hand over movie area, voice id hear but animation does not start

[Barak A. Pearlmutter]

The package already "Recommends: gstreamer1.0-gtk3" so by default it
will be installed; the system manager has to take explicit action to
disable automatic installation of recommended dependencies. And the
code should cough out some sort of error message if it tries to do
video and fails because gstreamer isn't installed; see the top of
src/classes/action/movie.vala. I'm open to adding something more
though. Um, patches welcome!