Make images zoomable in the Gallery post type

[igor-baiborodine]

Currently, the images are zoomable only if they are large enough and placed within the article post type. It would be nice to have zoomable images used in the Gallery-type post.

One way to implement this feature could be to implement a Gallery in a modal window, i.e., when a user clicks on the active slide in the slider, the gallery will be shown in a lightbox.

A possible implementation can be inspired by this thread on Stack Overflow: https://stackoverflow.com/questions/30775726/flexslider-with-a-popup-gallery

And the demo: https://jsfiddle.net/u8905s5x/8/