create a datalad repo for fmriprep files

[djarecka]

the files are used in test_newnode_neuro.py, for now can be found: https://www.dropbox.com/s/rrxc5kegeuzkbtr/fmriprep_test.tar?dl=0

[satra]

closing this as we should not be using any neuroimaging specific tests or data.