Twenty Fifteen: adding context to pagination links for screenreaders.

Props afercia, iamtakashi, fixes #30152


Built from https://develop.svn.wordpress.org/trunk@30316


git-svn-id: http://core.svn.wordpress.org/trunk@30315 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: improve appearance of page links when there are tons of pages to link to

Props iamtakashi, fixes #30301


Built from https://develop.svn.wordpress.org/trunk@30317


git-svn-id: http://core.svn.wordpress.org/trunk@30316 1a063a9b-81f0-0310-95a4-ce76da25c4cd