Tiled Gallery: Pass Carousel URLs through Photon.

Use `wp_get_attachment_image_src` instead of `wp_get_attachment_url` for `data-orig-file` in Tiled Galleries to trigger `filter_image_downsize` in Photon. This way the full image link in Carousel will point to an image served by Photon.
Merge pull request #523 from rase-/fix/carousel-full-image-link

Tiled Gallery: Pass Carousel URLs through Photon.