Make Tamland a tool

The Tamland repo currently contains two things:

1. A library of Python code that can be used to run a generic capacity planning report.
2. Instructions on how to create that report for GitLab.com, in files like book.yml (and the generated files in book/) and saturation.json.

We want to change this so that Tamland itself becomes independent of GitLab.com specifics. This means that all specifics need to become parameters of Tamland and moved outside of theh repository.

The goal is to be able to run Tamland for multiple environments, e.g. .com but also Dedicated tenants and perhaps more later.