BUG: Return a modifiable object or provide const

In order to match the basic Get paradigm, the Get*
functions must provide signatures similar to
the itkGet*ObjectMacro functions.

Change-Id: I5e43b7c1d03c13994e54b2d91b757368f29068a6
Merge topic 'MissedModifiableRefactoring'

49b702f BUG: Return a modifiable object or provide const