visual effects when changing slide

[piotr-s-brainhub]

visualEffectOnChangingSlide option passed to the carousel component with the following values:

• null (default) - no effects
• zoom - after slide switch, all the fully visible slides are zoomed in for 1 second, then zoomed out
• border - after slide switch, all the fully visible slides obtain a border for 1 second, the border has the BrainhubCarousel__visualEffectOnChangingSlide__border class, allowing to style it, as default it's solid 5px black

[frafra]

As #483 has been marked as duplicate of this issue, but I see no mention of fading behaviour, so I mention that in this message in order not to lose that suggestion.