Themes: Refine how we display the current theme.

props shaunandrews, kwight, matveb.
see #26003.

Built from https://develop.svn.wordpress.org/trunk@26681


git-svn-id: http://core.svn.wordpress.org/trunk@26571 1a063a9b-81f0-0310-95a4-ce76da25c4cd