Blog post on site revamp

This blog post goes into detail on a bunch of the stuff we did to revamp the site a few weeks back. It also includes made an IFTTT recipe to embed. 

I've listed @gboone and @meiqimichelle as co-authors, since they did lots of legwork in making all this happen. Remain very open to edits and suggestions!

This **depends on** #327, which is why it includes all of #327's commits. If #327 is merged, this PR will automatically shrink to just include the commits since then. That PR has to be merged first.

I've uploaded [a full-page screenshot](https://18f-public.s3.amazonaws.com/misc/new-site-post.png) of the post as captured on my computer, to make it easier to review in its rendered form.