Manual prev next bug

[mhulse]

                NextStep: function() {
                    $( '.stepDetails:visible' ).find( options.nextBtnClass ).click();
                },
                PreviousStep: function() {
                    $( '.stepDetails:visible' ).find( options.prevBtnClass ).click();
                }

I don't have time at this moment to do a PR.

Also, I was getting both steps showing when firing off "PreviousStep". So there could be more issues there.

I can try to do a PR soon if I find the time.