Change [quote] styling to Reddit/Github style (greyed out, with a bar on
the left side) instead of traditional forum style (big grey box around
the quote).
Reasons for this change:
* Box style is bulkier, especially for short quotes in comments.
* Box style works poorly for deeply nested quotes.
* Box style looks bad on widescreen monitors, since the quote stretches
across the full width of the screen.
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