Add ability to filter Ajax response to selector

I need the ability to filter the Ajax response HTML to a particular 
selector before displaying it in the modal.

In the documentation for Magnific Popup [Ajax Type](http://dimsemenov.com/plugins/magnific-popup/documentation.html#ajax_type), it states you should do this 
via the parseAjax method.

I chose to include the data-* on the anchor, since the target selector can
vary based on the resource.

Hopefully something to this effect can be worked into the code.

Thanks guys
One issue with this approach is that <code>this.currItem.el</code> doesn't exist when opening a Lightbox with JavaScript so will fail on line 211.