Introduce random config

[lyndseypadget]

This is a config-based, built-in alternative to proposals like this one. This PR addresses #1089, which is closed but perhaps worth reconsidering.

To enable:

            // Simply turning random on will use the entire range of top-level (horizontal) slides
            // Reveal.configure({ random: true });

            // Or you can specify an inclusive range of slide numbers
            Reveal.configure({
                random: {
                    rangeStart: 5,
                    rangeEnd: 8
                }
            });

            //Autoslide can be used with random
            //Reveal.configure({ autoSlide: 3000 });

Notes:

• Of course, random is off by default
• Can be generally enabled (true) or further specify a range of slides (rangeStart and rangeEnd)
• Slide range is inclusive
• Ranges can be manually overridden by any code calling navigateRandom
• Range will autocorrect if not in the proper order ([5,1] becomes [1,5])
• Random navigation will ensure you are not routed to the slide you're already on
• Can be used with autoslide on or off
• Randomized slides are always at the top (horizontal) level - never "basement" levels
• Fragments are still honored
• Transitions are only executed when navigating in a forward (right) direction

[bnjmnt4n]

Marking this as a duplicate of #1089 for now. @hakimel do you have any opinions about this?

[hakimel]

Thanks for the PR and taking the time to implement this. I said in #1089 that this didn't seem like a common enough use case, but judging by the number of votes on Stack Overflow I was wrong.

I'd be happy to add support for random order but I don't think this is the right way to do it. The slides should be moved into random order in the DOM instead, for two reasons:

• It'll be a lot easier to implement (just a few lines of JS to run at startup)
• it's a bit strange to have the slide numbers and progress bar jump around as they do when the DOM order remains unchanged

[hakimel]

Added what I mentioned above in 2625a92

It can be used as a config value Reveal.initialize({shuffle: true}) or called manually Reveal.shuffle().