Tweaks for Utility Page layout

[philgyford]

• Remove Sharing Buttons from Utility Pages
• This means there's no need for the right-hand "aside" column
• So we can make certain blocks – Embed, Raw HTML, Table and Image – the full width of the page at wider widths. Keeping the body text at the normal width (more readable than stretching it out to full width too).

For #372

[drcongo]

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