Adding implementation of GetInverse method for transform class.

If the transform is not invertable then an exception will be thrown.

Change-Id: I8ba1419bd2b09d98ffa69d5b30123bac361ac3d3
Adding doxygen documentation to the GetInverse method.

Change-Id: I7fed840ed61b9dd04f553c6de0763e357dff3dd0
Adding testing for transform's GetInverse method

Change-Id: I350b371770924d8a36b4dfafbbbb6f7cd6ed7580
Merge topic 'SIMPLEITK-573_AddAdditionalTransformMethods' into next

ed86f4a4 Adding testing for transform's GetInverse method
7bbb2dc6 Adding doxygen documentation to the GetInverse method.
35ca23b1 Adding implementation of GetInverse method for transform class.