Revision 1 of binary_tree_search_video.py

Rev 1: 12/16/2013
1) Improve automated tree graphic image design so that no node is displayed directly below its parent. 
    a) add invisible nodes, and invisible edges as placeholders to replace leaves that are not in the tree definition,
    b) change the default weight of edges to zero, so that displayed trees have freedom to spread out on the canvas.

2) Redesign the draw() method to support automated inclusion of invisible nodes when a left or right sibling is missing from tree, remove automated display of "root", "node", and "leaf" in the node label.

3) Redesign search routines BFS, and DEF so that drawing of graphic image information is not mixed in. Now new search routines can be designed solely on the merits of search.

4) Add a new search routine: DFSOrdered.

5) Add a new drawing routine: sketchTree. This routine adds the drawing information previously mixed into the search routines. Use this routine once to draw the full tree image during initialization

6) Change method blinkNodeTraversed color scheme to show a history of nodes searched in a new color.

7) Improve comments for accuracy.