Appearance Themes: Don't show theme actions if the current theme doesn't support menus or widgets.

props MikeHansenMe.
fixes #25949.
Built from https://develop.svn.wordpress.org/trunk@26335


git-svn-id: http://core.svn.wordpress.org/trunk@26237 1a063a9b-81f0-0310-95a4-ce76da25c4cd