Use custom error pages in cloudfront

[barlock]

Overview

As a user, I want to see a helpful error page when something goes wrong, so that I'm not confused or become distracted

Reference

• Cloudfront Custom Error Pages

Questions

• There's another issue for domain specific error pages, are those easy to do in this change as well? #26

Acceptance

• When a user gets a 404, they see a nice looking error page
• The user never sees a cloudflare specific error page

Tasks

• [ ] Design and create error pages
• [ ] Serve error pages on an error