Twenty Thirteen: update Genericons font files to latest version, 2.09. See #24595.

git-svn-id: http://core.svn.wordpress.org/trunk@24515 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: enqueue Genericons CSS from its own file, to allow for easier updates and maintenance, and to allow for better plugin overrides. Props obenland, closes #24595.

git-svn-id: http://core.svn.wordpress.org/trunk@24516 1a063a9b-81f0-0310-95a4-ce76da25c4cd