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

props ocean90.
fixes #26450.

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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.

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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
No-JavaScript and no-Customizer support for the new Themes screen.

JavaScript is rarely disabled, but graceful degradation is still important. For example, syntax errors can occur, usually with major WP updates that overhaul entire experiences and update external libraries combined with themes or plugins doing weird or old things. If this error is due to their current theme, a user needs to be able to access the themes screen to switch away from the theme. A more subtle issue could make things painful to diagnose.

This commit renders the grid in PHP (the template is duplicated, but it lightweight, fairly mundane, and easy to sync). On Backbone render, the grid is then re-rendered from JavaScript so searches can occur. Customize and Live Preview is disabled if JS fails to kick in. If JS is disabled, old-school "Preview" links are displayed.

No-Customizer support: The customizer is only supported when the browser supports postMessage (IE8+), and if the frontend is a different domain, CORS (IE10+). We use the .hide-if-no-customize class for this. Pre-customize "Preview" links should use .hide-if-customize.

The .load-customize class should be used to declare a link that opens the customizer. This enables customize-loader.js to intercept this link and load the customizer on top of the current window, making for a smoother experience.

fixes #25964.

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git-svn-id: http://core.svn.wordpress.org/trunk@26615 1a063a9b-81f0-0310-95a4-ce76da25c4cd
POT file update for Twenty Fourteen. see #26437.

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git-svn-id: http://core.svn.wordpress.org/trunk@26616 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove screenshotGallery. see #25948.

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git-svn-id: http://core.svn.wordpress.org/trunk@26617 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: Remove unused and untoggled no-js class.

props johnbillion.
fixes #26453.

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git-svn-id: http://core.svn.wordpress.org/trunk@26618 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Themes: Set a max-width on screenshots so they don't get blurry at very wide screen widths.

props matveb.
fixes #26172.

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git-svn-id: http://core.svn.wordpress.org/trunk@26619 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Add back CSS rules for RTL resize handles.

Disable CSSJanus' swapLtrRtlInUrl option, as we currently don't use it otherwise (and it breaks this if left on).

props ocean90.
fixes #26449.

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git-svn-id: http://core.svn.wordpress.org/trunk@26620 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Inline documentation fixes for `wp_heartbeat_set_suspension()`.

See #25073.

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git-svn-id: http://core.svn.wordpress.org/trunk@26621 1a063a9b-81f0-0310-95a4-ce76da25c4cd