Consider using Elastix registration as an alternative registration solution

[che85]

Would be nice to be flexible and be able to choose between different registration approaches.

As soon as Elastix is able to save rigid, affine and bSpline separately in a non proprietary format.

For the reference https://github.com/SlicerProstate/SliceTracker/issues/303

Steps to integrate Elastix into SliceTracker:

• [x] create initial rigid transform with General Registration (BRAINS):
• [x] harden transform for moving volume and label (make sure to invert and harden back to original ones afterwards!)
• [ ] resulting transform is: initial transform (BRAINS) * deformable transform (Elastix)
• [x] set inputs and masks in General Registration (Elastix)
• [ ] use Preset generic (all), but use the following ParameterFiles:

  <ParameterFiles>
    <File Name="Parameters_Rigid.txt" />
    <File Name="Parameters_Affine.txt" />
    <File Name="Parameters_BSpline.txt" />
  </ParameterFiles>

• [ ] apply registration
• [x] add option to select which registration algorithm should be used for SliceTracker registration (Brains, Elastix)
• [ ] add test for registration results

[fedorov]

This issue depends on https://github.com/SuperElastix/elastix/issues/18 to be resolved first.