[blog post] need to differentiate between blockquotes and asides

[Rich-Harris]

In docs, a blockquote is treated as a note:

In a blog post, it is treated as a quote:

But sometimes it should be a note...

...and sometimes it's neither:

[Conduitry]

When I navigate to the runes blog post from the list of blog posts, I see the quote icon as above - but when I refresh that page, it displays both icons superimposed, which is peculiar.

[dummdidumm]

Needed a blockquote without any fancy icon in #322 - added some thoughts on the code; I think it would be good to not render things differently depending on where you are and instead use classes to have different appearances consistently.