Help tabs: Update plugin install and media help text to reflect 4.0.

see #28654.

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git-svn-id: http://core.svn.wordpress.org/trunk@29416 1a063a9b-81f0-0310-95a4-ce76da25c4cd
About page, at last.

All strings are available for translation. We anticipate few, if any, changes before release. Images and video will be moved to w.org soon.

props ryelle, melchoyce, nacin, MarkJaquith, helen, DrewAPicture, kpdesign.
fixes #29243.

Built from https://develop.svn.wordpress.org/trunk@29643


git-svn-id: http://core.svn.wordpress.org/trunk@29417 1a063a9b-81f0-0310-95a4-ce76da25c4cd