allow counter update for inline elements

this makes magnific popup update the "x of y" conter in inline items that contain an element of class mfp-counter

more rationale: http://stackoverflow.com/questions/25527101/magnific-popup-gallery-how-can-i-display-a-counter-in-an-inline-type-item/25580964
It actually is related, because calling ```_parseMarkup``` in this case will not yield a result when calling ```template.find(EVENT_NS + '-'+key)```.
But it is arguably not very nice style.