Twenty Thirteen: fix toggling header text display in Customizer. Props obenland, fixes #23722.

git-svn-id: http://core.svn.wordpress.org/trunk@23670 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: better styles for gallery captions. Props obenland, see #23584.

git-svn-id: http://core.svn.wordpress.org/trunk@23671 1a063a9b-81f0-0310-95a4-ce76da25c4cd