Twenty Fourteen: limit back compat to 3.6 and later versions. See #26055, props obenland.

git-svn-id: https://develop.svn.wordpress.org/trunk@26225 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fourteen: fix an issue with keyboard navigation where you couldn't navigate to the previous image. Props obenland, see #25946.

git-svn-id: https://develop.svn.wordpress.org/trunk@26226 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fourteen: general cleanup for spacing, inline comments. Props obenland, see #25946.

git-svn-id: https://develop.svn.wordpress.org/trunk@26227 602fd350-edb4-49c9-b593-d223f7449a82