Module tree

Package: 
Module : 
This module provides 4 classes. TK based GUI (graphical user interface) of
1) tree-view
   The tree view is designed to display hierarchical data structure.
   each level of the tree can be expanded / collapsed to show / hide subtree
   one or more items of the tree could be selected by mouse click

2) list-view
   The list view is designed to display a list of objects
   each item in the list can be locked (to prevent deletion) and unlocked
   the list is mainteined by FIFO principle (first in, first out), unless locked by user