ipython notebooks for nbviewer added

Added some new notebooks and only made a few modifications to the existing example notebooks. Removed some extra image files that didn't seem to be needed. Reorganized so that all notebooks sit in a single 'WWW' directory, and use data from a single 'data' directory. There's also a 'alt_versions' directory with notebooks we might combine with existing notebooks, spin off into their own, or just delete.

Let me know if you don't agree with the directory reorganization.