add anatomical processing from fmriprep

[akeshavan]

we need to add anatomical processing if freesurfer hasn't been run. Let's use the same one as fmriprep: https://github.com/poldracklab/fmriprep/blob/master/fmriprep/workflows/base.py#L409-L466

[richford]

Use smriprep for inspiration. Or simply throw an error and point the user to docker run smriprep.