Gets the data object that was passed to a lightbox.
Retrieves the data object, if any, that was passed when a lightbox
was opened via the openLightbox() method.
If a lightbox was opened in any other way, getContext() returns undefined.
To pass data to a lightbox, it must be opened programmatically using the openLightbox()
method. Lightboxes that are opened automatically on page load, or via a link from a page element don't receive passed data.