Rich output + interact + widgets

- Moved rich output, interact, and widget tutorials over from IPython in-depth
- Updated interact demo with new widget names
- Updated widget exercises with new styling API
- Audited the exercises for all three contents
- Merged the interact and widget tutorials into one jumbo "Widgets.ipynb" notebook.
- Added a San Francisco expenditures Pandas/interact example to the widget/interact notebook.

This is tons of content and I definitely won't cover it all.  I included extra just-in-case...  I'll keep track of how far I get in the 2:45 min session.  I'm planning on working the demos out live in front of the students.