ENH: BRAINSLandmarkInitializer works with multiple transformTypes

The BRAINSLandmarkInitializer has changed to support different transform
types after the recent changes to the itkLandmarkBasedTransformInitializer
class:
http://review.source.kitware.com/#/c/17847/

Based on new changes, an input flag is added to define the output
transform type:
--outputTransformType

This flag is defaulted to the AffineTransform (the only option that
existed before), and now can support VersorRigid3DTransform and
BSplineTransform too.

If BSplineTransform is chosen, we also need to use the following added
flags to define the parametric domain for the BSpline transform:
--inputReferenceImageFilename
--bsplineNumberOfControlPoints