Adding preliminary displacement transform interface

Change-Id: Ie3d689bc9d4396a2ee37020bba7b19135f2f4f9c
Adding additional PimpleTransform method for SetIdentity

The smoothing specific displacement field transforms, needs
specialized SetIdentity methods.

Change-Id: I98714a1ab9ad623ae2e9522feba281d3cc338e37
Adding MakeUnique before set methods are called

Change-Id: Ibaff8e604b41b7ff1ce5896c1e83c46c61d863b9
Implementing Setting of smoothing parameters and interpolators

This interpolator is simply created from the valid interpolator
enums.

The smoothing parameters are handled in a new way. Because different
smoothing algorithm require different ITK displacement filed types,
when the smoothing parameter is set and is different, the methods
create a new ITK DisplacementFieldTransform and sets the new
displacement field to the old one, and then sets the new smoothing
parameters.

Change-Id: If5f60739b6ffb7a74ddbb61809fb29247a6357e2
Merge topic 'AddDisplacementFieldTransform' into next

61fa218b Implementing Setting of smoothing parameters and interpolators
ac02d9ad Adding MakeUnique before set methods are called
a5e25a3d Adding additional PimpleTransform method for SetIdentity
3021b913 Adding preliminary displacement transform interface