WIP: BRAINSFit with Euler3D as the rigid transform

On this version, the "versorRigid3D" transform is replaced by
"Euler3D" transform that has more consistency with ITKv4 since
versor optimizers are not implemented in ITKv4 yet.

This version of BRAINSFit works pretty well on affine and rigid
transforms.
BRAINSFit without VersorRigid transform is useless, but I committed the current changes
as they may be used some time, or be a good guide for adding new options to BRIANFit later.