Define footprints for Viade folder structure

Given that there is some interest in definig a common structure for the viade folders, maybe we could consider defining the structure using footprints. Here is a [blog post](https://ruben.verborgh.org/blog/2019/06/17/shaping-linked-data-apps/) the justifies the need for footprints and shapes.

There is a draft introduction to footprints [here](https://janeirodigital.github.io/footprints/primer) and a formal specification [here](https://janeirodigital.github.io/footprints/spec).

Start by reading the linked footprints primer and formal specification, then inspect the Viade data model specification for the folder structure. No repository files, tests, or entry points are named. Done would require an agreed footprints-based definition of the common Viade folder structure.

Written by the indexing model from the issue text.