[BUG #5313] - Use overflow:scroll / -webkit-overflow-scrolling: touch; in iOS5 instead of iScroll (edit)

* Check for NativeScroll did not work.
Code Formatting
[BUG #7058] Use double-sized resolution images for Retina Display

* Refactoring of overlay creation
* Prevention of loading the medium resolution image, if a high resolution image was chosen.