Fine-tune typography on blog posts

Created by: quinnkeast

This is a quick set of improvements to typography and spacing for the blog posts. Changes only target the blog posts themselves. This will make our blog posts more readable for all users.

gatsby-remark-images has a nasty habit of wrapping <img> elements in <p> tags, which causes trouble with having a narrower paragraph elements without affecting the images. I've added gatsby-remark-unwrap-images to the gatsby-config.js to avoid this. As far as I can tell, this only affects the blog posts, which is what we want.

I've also made a couple of tiny formatting tweaks to @efritz 's latest blog post to un-hacky-workaround the blockquote formatting and make the linked image render properly. I checked through a handful of older blog posts and confirmed nothing appears broken.