Add component for Xarray's HTML REPR

[jhamman]

Many of the blog posts here benefit from showing Xarray's REPR in the post. It would be great if we can hook up a React component that makes including the HTML repr as easy as possible.

[jhamman]

This is how we do this in Pangeo-forge: https://github.com/pangeo-forge/pangeo-forge.org/blob/2fe516f88db8426d1b49f40f0382fc01d007bdeb/src/components/dataset/repr.js#L41

@andersy005 - do you have ideas for how we want blog authors to produce and/or sanitize their HTML.