Add icon to the help button in distraction-free writing.

props ocean90.
fixes #26450.

Built from https://develop.svn.wordpress.org/trunk@26722


git-svn-id: http://core.svn.wordpress.org/trunk@26611 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Un-translate all of the about page strings so translators don't start working on incomplete copy. see #26387.

Built from https://develop.svn.wordpress.org/trunk@26723


git-svn-id: http://core.svn.wordpress.org/trunk@26612 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use p.description instead of <small> on the discussion settings page. see #26441.

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git-svn-id: http://core.svn.wordpress.org/trunk@26613 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Map old -width theme tags to new -layout tags for the purposes of translation in the admin.

see #21442.

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git-svn-id: http://core.svn.wordpress.org/trunk@26614 1a063a9b-81f0-0310-95a4-ce76da25c4cd