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. Retargeted from #378.
Gotcha. So the benefit of using the `rax_keypair` module instead of how we do it today is that all we need is the private key locally. We don't need to have the public key uploaded to the right region as a pre-requisite since `rax_keypair` can do that for us. Am I (finally) understanding this right? ;)