Problem with Ajaxed Content and Unveilhooks

[JamesToothill]

Describe the bug
When applying data-script to an element that is later re-added with ajax the lazyloading class sticks and the new element is never 'lazyloaded' I believe it to be related to #799 as I believe the callback function is never reached and therefore 'lazyloaded' never triggered as the script already exists in the dom and therefore is not re-added, I'll add a PR to fix this myself..

To Reproduce
jsfiddle.net

Steps to reproduce the behavior:
See JS Fiddle

What is the expected behavior:
Element would lazyload correctly

What happened instead:
Element does not lazyload