Update lightbox to have autorotation and configurable options.

I needed to be able to modify the lightbox options but I didn't want to have to modify the source.

As a change I moved the options out of the anonymous function scope to make them globally accessible. I can now override them in my app.

I also needed an autorotate feature.

I consolidated the next and prev logic into two new prototype functions, next() and prev() and replaced them in several places. I also add a prototypal autoSlide function that operates on a timer, and then cancels itself on any input from the user (i.e. click, keypress).

Let me know what you think. Thanks for the awesome library!