Support both "demo" and "test" modality

[tcompa]

We could add an env variable that can be e.g. "test" or "demo".

When set to "test", we run everything as it does currently.

When set to "demo", we skip several of the current steps. This is to be defined, but an example of the "demo" modality could be:

1. We copy images into known paths
2. We collect tasks.
3. We create project/datasets/workflow
4. We do not run the job - so that the user can do it from the web interface
5. We fully skip example 02.

[tcompa]

This is made obsolete by the recent split into testing vs. examples. We can have more specific discussions on what we want a "demo" to look like elsewhere.