Assemble static assets in CI

[mblayman]

If Circle CI can run webpack, then that gets a step closer to having no Node in Ansible.

• [x] Run webpack in CI
• [x] Upload assets as a tarball to S3.
• [x] Add asset to deployment.
• [x] Check if directories need executable bit.
• [x] Test that it works by checking the site.
• [x] Remove static_root and test again.