Data: Use datalad to install

[Lestropie]

The workshop data that currently has public visibility at https://osf.io/sn9bk/ has been uploaded via DataLad. However I've not been able to download those data using DataLad from any system. I suspect there's a bug in the DataLad OSF extension; from memory it was an unhandled exception trying to run a less-than operator on a NoneType. So for the time being, those data are being downloaded as zips with convoluted URLs. Longer-term, want to not only use DataLad to do the download, but also there will be a "master" DataLad dataset that contains the various sub-datasets (single subject data, dwifslpreproc, FBA) as children, and in construction of the image the whole lot can be fetched in one command.