This adds two hypothetical variants to the Mu demo, "building" new capabilities
up from the basic Express and MongoDB app we start with:
1) The first variant is to leverage the Mu SDK for service discovery and
configuration, eliminating the "loosely typed" approach that is common with
Docker (e.g., having to fetch connection URLs from arguments, environment
variables, etc). This extends the Mu type system "into" the Docker container,
whereas previously it stopped at the boundary.
2) The second variant really takes this to the next level, embellishing the nice
DSL-like approach. In this model, infrastructure is expressed in code.
Instead of manually creating a volume, we will arrange for the mongodb/mongodb
to auto-mount a mu/x/fs/volume, as per [the cloud-neutral design doc](/docs/xcloud.md).
This just adds a simple voting app for the demo script. It leverages
a Node.js Express app for the frontend and a MongoDB database for the backend.
It conditionally provisions and attaches to an AWS Elastic Block Store volume
in the event that it's targeting an AWS cluster, and ephemeral storage otherwise.
