Extract first video or image from Video and Image post format posts, and place the item above the title within its own HTML wrapper with `the_video()` and `the_image()'. Also, remove the item from the post content with `the_extra_content()`.
This allows us to meet the design requirements for Twenty Thirteen with minimal changes to the theme template files. Fixes#23620.
git-svn-id: https://develop.svn.wordpress.org/trunk@23820 602fd350-edb4-49c9-b593-d223f7449a82
