Real-time update of the cursor information v2

Issue : https://med.inria.fr/redmine/issues/1741

Goal :  automatically update cursor information (X, Y, pixel value) while moving the mouse.

After a mouseEvent, a new vtkImageView2DCommand is invoked, that indirectly launches vtkImageView::UpdateCursorPosition.

The mistake of the first version was to use an existing Command (RequestedPositionEvent) that was already used for other purposes.
Hints : last time, bugs appeared with the Custom View (with Sagittal, Axial, ...), by linking the position and moving the mouse.It was modifying the slices of the views.