Twenty Fifteen: add instant updating of color schemes to the customizer with postMessage.

Props celloexpressions, bradyvercher, westonruter, fixes #29988.



Built from https://develop.svn.wordpress.org/trunk@30274


git-svn-id: http://core.svn.wordpress.org/trunk@30274 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: updates to customize-preview.js missed in r30274.

Props celloexpressions, See #29988.


Built from https://develop.svn.wordpress.org/trunk@30275


git-svn-id: http://core.svn.wordpress.org/trunk@30275 1a063a9b-81f0-0310-95a4-ce76da25c4cd