Twenty Fifteen: clean up sprintf from template tags and use the correct escaping for twentyfifteen template tags.

Props aprea, obenland, fixes #30319


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git-svn-id: http://core.svn.wordpress.org/trunk@30311 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use a brighter blue against dark backgrounds in the admin menu and toolbar.

Not only does this pass contrast guidelines, but it also visually appears closer to the original highlight blue used against light backgrounds.

props melchoyce. fixes #30323.

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git-svn-id: http://core.svn.wordpress.org/trunk@30312 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: adding context to page links for screenreaders.

Props afercia, fixes #30174.


Built from https://develop.svn.wordpress.org/trunk@30314


git-svn-id: http://core.svn.wordpress.org/trunk@30313 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: since color schemes can be customized let's call them base color schemes instead of just color schemes.

Props celloexpressions, iandstewart, fixes #30316


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git-svn-id: http://core.svn.wordpress.org/trunk@30314 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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