Revision 217

* Thuban/UI/tree.py (color_string): Removed. No longer used.
(SessionTreeCtrl.update_tree, SessionTreeCtrl.add_items): Split
update_tree into update_tree and add_items. The tree now uses a
more generic way to display the contents of the tree.
(SessionTreeCtrl): Add a doc string explaining the TreeInfo method

* Thuban/Model/layer.py (Layer.TreeInfo),
Thuban/Model/extension.py (Extension.TreeInfo),
Thuban/Model/map.py (Map.TreeInfo),
Thuban/Model/session.py (Session.TreeInfo):
Add TreeInfo methods to implement the new tree view update scheme