Revision 2 of binary_tree_search_video.py

Rev 2: 12/23/2013
1) Provide 3 tree generation options: manually create tree, generate random unbalanced tree, create balanced tree
2) Improve draw method to include left, right, and middle "invisible" nodes and intelligent edge weights,
#            now all edges in same direction are parallel, and every node of the same depth is displayed at the same depth
3) Fix bug in DFSOrdered() search function
4) Provide an initiallization segment near the top of the code to simplify control of tree sketching and search animation
5) Clean up PNG image display code
6) Improve video scaling: 
           a) support large trees
#            b) support HD video during graph generation and in FFmpeg for 1920 x 1080 pixel size
       New FFmpeg command line to generate intelligently scaled video in HD from PNG image sequences:
        ffmpeg -f image2 -r 1 -start_number 00001 -i bst_graph%%05d.png  -b:v 5000k -vcodec mpeg4 -r 30 -vf scale="'if(gt(a,4/3),1920,-1)':'if(gt(a,4/3),-1,1280)'" -y movie.mp4