Basic schema for a dataset as a collection of files

[jsheunis]

This mostly follows the convention defined at https://docs.datalad.org/projects/tabby/en/latest/conventions/tby-ds1.html

At the moment it's just a linkml version of the same tby-ds1 convention, with minor tweaks to the inclusion/use of some ontologies, and it has the additional classes: NamedThing and DatasetCollection which I kept from the cookiecutter template.

I haven't checked if data validates with this. This is just to provide a first iteration, and it will definitely need to be changed in order to get to the goal of supporting all datalad dataset properties as well as RO-crates.

[jsheunis]

Build failure is caused by this issue: psychoinformatics-de/datalad-concepts#59

[UPDATE]: This has been "fixed" by commenting out the offending lines (95c5c8b), i.e. delaying the problem to be fixed.

[jsheunis]

Now that the test succeeds, I will merge this so that we at least have a minimal working example of a schema project in place that somewhat resembles a datalad dataset.