Two new fragment functions to check for next & prev without actually navigating

[mikemellor11]

Needed for the use case below:

Reveal.addEventListener( 'fragmentshown', function( event ) {
    if(!Reveal.isAutoSliding()){
        Reveal.configure({autoSlide: 400});
    }

    if(!Reveal.hasNextFragment()){
        Reveal.configure({autoSlide: 0});
    }
});