[wip] Use Ansible instead of a shell script to deploy the site from Jenkins.

Use it to manage the deployment and configuration of the node.js backend (#375) as well.
> With this change, it looks like we would be building the site on each web server.

Nope! The `push.yml` playbook uses a `local_action:` to invoke `build_site.sh` on the Jenkins host.

> If so, we need to remove the ./build_site.sh invocation from this Jenkins job configuration file (lines 38 - 40). Same goes for the build_staging_site job configuration file as well.

Ah, I did miss this though, thanks for the catch! If I do stick with using Ansible here I'll take that out.