Make Twenty Fourteen the default theme. props markmcwilliams. fixes #25702.
Built from https://develop.svn.wordpress.org/trunk@26024


git-svn-id: http://core.svn.wordpress.org/trunk@25955 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: add full-width featured images for layouts without a content sidebar, but use `wp_is_mobile()` to load smaller-sized images for mobile. Props iamtakashi, fixes #25758.
Built from https://develop.svn.wordpress.org/trunk@26026


git-svn-id: http://core.svn.wordpress.org/trunk@25956 1a063a9b-81f0-0310-95a4-ce76da25c4cd