Adding GetInverse method to transforms

This is a wrapper to the itk::Transform::GetInverse method. However,
it replaces itself with a new transform the same type as the current
with the same PimpleTransform interface.

Change-Id: I183898e9c83e0a2d31c846ec001e91c73636bc4b
Adding doxygen comment for SetInverse

Change-Id: Id1b6300d6bf2ece7f4c281d22f03bf654e85f2a2
Adding comprehensive testing for GetInverse method

Change-Id: Ie4db44de042c1beef81f7d554ffd64b9b63741cf
Adding missing declaration of GetInverse in PimpleTransform base

Change-Id: Ic368e3b86fd256fed005095d5c2ba73ab61bbada
Adding Transform::IsLinear method

Change-Id: I3e904c7b05083d1b9c67b9c664f7502293493bd7
Merge topic 'SIMPLEITK-573_AddAdditionalTransformMethods'

9336a7c4 Adding Transform::IsLinear method
09f80fad Adding missing declaration of GetInverse in PimpleTransform base
98b38a5d Adding comprehensive testing for GetInverse method
5d4447e5 Adding doxygen comment for SetInverse
501ea0b9 Adding GetInverse method to transforms