Twenty Fourteen: implement UX features in spite of being non-standard CSS selectors that won't validate. `@viewport` for a better touch experience on Windows, and `::selection` for better text selection styles. See #25888 and #25898, props celloexpressions.

git-svn-id: https://develop.svn.wordpress.org/trunk@26069 602fd350-edb4-49c9-b593-d223f7449a82
Bundled Themes: implement Microsoft-specific `@viewport` rules for better responsive styling in Windows 8 "snapped" views. Props celloexpressions, fixes #25888.

git-svn-id: https://develop.svn.wordpress.org/trunk@26070 602fd350-edb4-49c9-b593-d223f7449a82