[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. 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.