View refactor 2

Ok so I tried to continue the good job Olivier and Flo had started with the view refactoring.
First, I had to rebase so I hope I didn't break anything doing it...

Now, all the diffusion toolboxes should be operational and appear only when necessary.
Just 1 or 2 questions:
- The new medVtkView is currently only used in the medRegistrationWorkspace. Should we use it everywhere (see medViewContainer::open) ?
- After an action in a toolbox (fiber, tensor,...) the view needs an update. Should this update be done in the toolbox or in the interactor? Right now it's not really clear, and done in one or this other...

Besides that, I think this PR should be quite ready to merge.