With the recent addition of search_embed iframes on other pages, we
had photo cards appearing but the photo_clipboard module was not
imported thus the checkboxes did nothing. I don't want to import
photo_clipboard onto every single page, I'd rather they click through
to the full search UI. Otherwise every single page will have the tray
and often not a good enough reason for it.
So, since the functionality of the checkbox is completely reliant on
the photo_clipboard.js module anyway, there's no reason not to have it
generated by that module.