ADD: Support for DisplacementField transform in TubeTransform.

ADD: Added support to apply a displacement field to a collection
     of spatial objects in TubeTransform.
ENH: Handling of transform reading in TubeTransform; Support for
     inverse transform as a command-line argument; Currently
     supported transforms are Affine, VersorRigid3D and
     MatrixOffsetTransformBase. This covers the affine and
     rigid transforms produced by BRAINSFit and also the affine
     transforms produced by ANTS for instance.

     Displacement fieds can now be provided as an argument to
     --displacementField. These displacement fields have to
     be compatible with the way ITK handles displacement fieds,
     though. E.g., using the displacement fields produced by
     ANTS works fine. Also, there is currently no support to
     compute the inverse displacement field - Hence, the user
     is responsible to supply the correct one.
ADD: TubesToImage code which produces a binary image of tubes
     that can easily be visualized and overlayed on other images
     without the need to display the spatial objects themselves.
FIX: Added a check before CovariantVectors are transformed in
     the itkTubeToTubeTransformFilter.

Change-Id: Ia49dd1722b968269cab7207d5cff00f6da84878f
ADD: TubesToImage application to generate binary images from tubes.

STYLE: Incorporated Jamie's comments in TubeTransform

Change-Id: I95ab0b5735a8cec0f3196cb0f33ce576abb8dede
ENH: Use generic itk::Transform in TubeTransform insead of specializing.

FIX: itkTubeToTubeTransformFilter NEEDS a transform from the user, set
     by SetTransform() - Previously a new (empty) transform was instan-
     tiated if m_Transform was 0.

Change-Id: I1e44d36a874befc4cec256f8293bd0841f02489d
ENH: Added Jamie's comments to TubeTransform

Change-Id: I5fa2ade7f9a4535afb55d7989f3a6d0a1c4e7184
Merge topic 'rk-TubeTransformExtension'

6785c8e ENH: Added Jamie's comments to TubeTransform
8906b4b ENH: Use generic itk::Transform in TubeTransform insead of specializing.
08cdc92 ADD: TubesToImage application to generate binary images from tubes.
91f0f74 ADD: Support for DisplacementField transform in TubeTransform.