ENH: Added support for thin plate spline transforms

Added full support for thin plate spline transforms:
* save/load forward and inverse transform from ITK files
* verification that ITK and VTK thin plate spline transform computes exactly the same values
* basic storage and inversion tests

Thin plate spline transform is used by the Landmark Registration module, so now the computed transform can be saved to the scene or exported.

From: Andras Lasso <lasso@queensu.ca>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23826 3bd1e089-480b-0410-8dfb-8563597acbee