Add a hierarchical tree structure component

[jacques-lebourgeois]

On the Orange LiveObject project, we have a hierarchical tree structure, either as a menu on the left, or in a dropbox in a form or in a filter bar. We don't find this type of component in boosted v4 and think it could be a good added value to have this type of component. Indeed, presenting a tree structure of groups, directories... is a rather common need in business applications. I put in copy screen an example of what we currently have in our project.