Tiled Gallery: Pass image dimensions to Photon.

Image dimensions are now passed to photon (even though they are stripped) so that they can be determined by Photon more easily
Tiled Gallery: Only setup new galleries on events.

Previously all Tiled Galleries would be found and set up again if any new galleries could appear through, e.g., an Infinite Scroll event. Now we only look for new galleries, and don't reinitialize the existing ones, so that we also don't set multiple copies of the hover effect (for captions).
Tiled Gallery: Updated outdated comment.
Tiled Gallery: Better wording in comment.
Tiled Gallery: More whitespace.
Tiled Gallery: Fix border width computation.

To make sure that border width is computed correctly, we have to be sure to get border-width instead of the entire border css.