ENH: Replace python print with print() function

This is needed for python 3 and is backward compatible with python 2.7 and 2.6.

Some prints were commented out, I just added the parantheses, to be consistent throughout the code.

I did not update:
- gdcm Python files (third party)
- notyetusable Python tests, those need refactoring anyway
- the Python examples, they are being moved to the itk examples repo

Change-Id: If527aacb1c379165c2188dfa8f85c28ed55ed4c9
Merge topic 'Python3Print'

621872a2 ENH: Replace python print with print() function