Bring keyboard accessibility to the theme install screen and theme action buttons. props jorbin. see #27521.

Built from https://develop.svn.wordpress.org/trunk@27804


git-svn-id: http://core.svn.wordpress.org/trunk@27638 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Set baseline colors for the light playlist skin. props kwight. fixes #27562.

Built from https://develop.svn.wordpress.org/trunk@27805


git-svn-id: http://core.svn.wordpress.org/trunk@27639 1a063a9b-81f0-0310-95a4-ce76da25c4cd