Twenty Fifteen: correct list indentation in older IE versions.

Props iamtakashi, fixes #30074.


Built from https://develop.svn.wordpress.org/trunk@30012


git-svn-id: http://core.svn.wordpress.org/trunk@30012 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: valid HTML for accessible child page menu expanding and collapsing -- now with even better accessiblity.

Props afercia, davidakennedy, iamtakashi, fixes #30083.


Built from https://develop.svn.wordpress.org/trunk@30013


git-svn-id: http://core.svn.wordpress.org/trunk@30013 1a063a9b-81f0-0310-95a4-ce76da25c4cd