BUG: remove itkVersorTransformOptimizerv4 from BRAINSTools

Based on the last version of ITK, the VersorTransformOptimizerv4
is removed from ITKv4, and its usage should be replaced by newly added
RegularStepGradientDescentOptimizerv4.

This patch addresses the above issue, so now we can
build BRIASTools based on the last version of ITK without any compiler
error.
Merge pull request #88 from aghayoor/removeVersorOptFromBTools

BUG: remove itkVersorTransformOptimizerv4 from BRAINSTools