Twenty Fourteen: improved JS support for keyboard navigation for main navigation menu. Props obenland, see #25054.

git-svn-id: https://develop.svn.wordpress.org/trunk@25757 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fourteen: improve display for elements in the featured content area by preventing titles from breaking and letting content overflow with an ellipsis. Props obenland, fixes #25053.

git-svn-id: https://develop.svn.wordpress.org/trunk@25758 602fd350-edb4-49c9-b593-d223f7449a82