The lightbox will now distinguish between whether or not something is a
photo and a YouTube video by the class name of the message inline
preview. It embeds the YouTube video in the lightbox as an iFrame
rather than previewing the video screenshot.
This includes reduced title font size to bring the total info bar
height to the same height as the buttons, and an image preview that
doesn’t hit the walls of the container.
This adds an event listener (by way of delegation) to the
.message_inline_image elements that pops up the overlay and hides it
when the overlay exit is clicked.
Fixes#654.
Brock Whittaker