Updated vtkProject.
Added loadFromList and saveToList functions.

Not unit tested. Will test the final effects after.
But it looks like it works.
Corrected "before root" instead of "root" folder.

The aim is to avoid redundancy : the root path of a project shall be
$beforeRootFolder\$projectName.
vtkProject stays a "string generator", and only the relative path of the
xml sheet does not depend on the name.
It may be useless, some advice would be appreciated on the design.
Passing prep run.