Adding casting to itkImages for Image inputs types

The following convention has been used in ITK, the filter input image
is of type "InputImageType", and is set with SetInput, while the
additional inputs have SetNameImage.

SimpleITK is establishing the conventions of having Image as a suffix
to ensure the user know the expected type.

Change-Id: I803a6a4a9821a4289edfa37c8a336ded407b903f
Merge topic 'SIMPLEITK-429_AddOptionalInputs' into next

51f661e9 Adding casting to itkImages for Image inputs types