Precache Images
This commits precaches an image to the left and an images to the right for each slider using Flutter's precacheImage function.
This merge request is currently in draft mode, because I'm not happy with the separated slider classes. My plan is to merge the two or the three classes into a single class.
I've merged all the functionalities of each carousel slider widget into a single CarouselSliderBox
widget.
Fixes #68 (closed)