Based on iOS Tech Talk 2013 - Architecturing Modern Apps Part 1. Refer to video at https://developer.apple.com/tech-talks/videos
Copyrights belong to Apple.
============= Fork of https://github.com/devonc/Custom-Transitions
Modified the Drag to Dismiss Transition, added support for non-interactive animations and reversed animation for presentation.
Modified demo to support A Navigation Controller and Modal View Controller presentation.
Added support to allow for interactive dismissal on top of a UIScrollView.