* Port the dotenv file to a real shell script. Shell scripts are more
  portable as they don't require the installation extra dependencies.
  They also have proper support for double and single quoting and
  better support for variable expansion, which is not the case for many
  dotenv implementations (I'm looking at you docker-compose)

* Rename many variables, adding the `DEMO_` prefix. This is to make it
  more clear which variables are fixtures for demonstration purposes.

* Add a number of new new variables and corresponding templates. Mostly
  to allow us more customization of the demonstration fixtures when
  bootstrapping