ITK developing branches

Hi all,

This is a branch to study and discuss the switch the public medinria project to ITK 4. This branch shouldn't be merged as it is since it contains hard links to various branches that really implement the switch. That being said, it's a nice starting point for discussion.

See https://med.inria.fr/redmine/issues/1314 for some more info on what's been done and what's left.