Allow 2 slides to display continuous

This merge request will allow to continuously loop 2 slides.

I totally understand reasoning behind not allowing to loop through one image (slide).
But this logic don't apply for 2 images. You actually can and, in my case, need to loop them.

Overall this functionality about not allowing to loop 2 images is actually a feature that needs to be moved into configuration parameter (example: this.options.minSlideCountToLoop = 2)