AppGyver employee here! There is currently no native support for changing between WebViews with a slide motion, but I created a GitHub issue on the subject that you can follow.
Also, for image galleries etc. there are plenty of CSS/JS solutions that work alright, e.g. http://swipejs.com/ or http://onehungrymind.com/build-sweet-angularjs-photo-slider-pt-2-ngtouch/