[Feature] Expose points-based registration

[adamltyson]

For some of the more complicated registration problems, it would be useful to expose Elastix's Point-based Registation. In theory (famous last words), it shouldn't be too hard to create a workflow by defining points in napari, and then adding an additional metric to take these into account.

[thisisrick25]

Hi @adamltyson can you give some advice on how to approach this?

[adamltyson]

I think this issue may be fairly complex. TBH I don't think it's likely the best issue for a first time contributor to the repo.

[IgorTatarnikov]

This example seems to outline the steps really well. We should either accept paths to corresponding points (stored in an ITK readable file) or by taking a pair of points layers from napari indicating corresponding points and transforming them in memory to an ITK compatible form.