[WIP] Adding options conducive to small animal neuroimaging

[rciric]

• Use of Laplacian alignment as a criterion during the final (CC-based) registration stage is made optional.
• The bspline_fitting_distance is measured in mm. The default setting of 200 can become problematic when images have a smaller FoV, as is often the case in small animal neuroimaging. Thus, setting this value is also made available as an option.

[oesteban]

Hey @rciric, can I ask you to send this PR to https://github.com/poldracklab/niworkflows/blob/13a7ff07fd1f7188823f5e60cf339e0e1787076d/niworkflows/anat/ants.py instead?

We will synchronize this with your updates here, but for now I'd say niworkflows should be the place where we develop this workflow. We will use niflows just for testing.