Add sample data set(s)

[lassoan]

Official freesurfer sample data set is 8GB. This is quite extreme. It is also quite odd that they describe 3 linux commands to download a package instead of simply posting a download link (strange people...).

It would be much better for users if we made available one or few sample data sets in SampleData module.

You can prepare a nice scene, save as mrb, and upload it as Release asset in the repository (create a "Data" release and upload all sample and test data there). You can write SampleData plugin similarly to this: https://github.com/SlicerRt/Sequences/tree/master/SequenceSampleData