Add option to allow zoom animation

[arnowelzel]

Also see https://wordpress.org/support/topic/zoom-animation-when-opening-the-lightbox/

Zooming the images for opening animation is not supported as this does not work very well with squared thumbnails in Wordpress. However, some people may like to use with smaller images which are not squared thumbnails.

Todo:

1. Add option in the backend
2. Implement getThumbBoundsFn() in the frontend and set options for Photoswipe if zoom animation is enabled

[afmklk]

Would definitely appreciate this. Should work quite will if thumbnails are not cropped.