Fix blockquote styles

[Krinkle]

I'm looking to add blockquote styles to Amethyst for use in the QUnit docs on https://api.qunitjs.com/QUnit/load/#karma-runner, where there is currently an unstyled blockquote.

Looking at jquery-wp-content for inspiration, I noticed the styles are quite odd.

For example: https://meetings.jquery.org/2013-01-31-tc39/#map-set-comparator (scroll down slightly) renders today as:

Notice that:

• The font seems disproportionally large.
• The background shade is applied to each line separately instead of to the block as a whole.
• The list doesn't seem part of the quote.
• The bold text is receiving its regular text color override instead of inhering the quote text color.

In the doc sites, I could not find any other pages that uses blockquotes. We do have various blog posts with quotes though, such as:

https://blog.jquery.com/2016/07/27/the-jquery-foundation-and-standards-2/

[Krinkle]

After:

Doc example	Blog example