ENH: adding the DistancePreservingRigidityPenalty term

Contributed by J. Kim, M. M. Matuszak, K. Saitou, and J. Balter

Based on their paper
Distance-preserving rigidity penalty on deformable image registration of multiple skeletal components in the neck
Medical Physics, vol. 40, no. 12, pp. 121907-1 - 121907-10, December 2013


git-svn-id: https://svn.bigr.nl/elastix/trunkpublic@4800 4d348492-3962-11de-aa85-65a2020054a3