Removed these features that make sense in a presentation slideshow
(e.g. during a talk) but that are potentially confusing during
a passive slideshow like Calamares has:
- Using 'c' blanks the slideshow.
- Entering a slide number + enter changes slides.
- Add a NavButton, which shows a directional arrow, and fades in on hover.
It can be used left- or right- by setting an image source
and click handler.
- Specialize NavButton to Forward and BackButton.
- Add a SlideCounter navigation aid.