Major refactoring of saving, notification....
Major refactoring of saving, notification.
* Refactored the save widget so that the notebook doesn't depend
on it. Now the notebook emits events and the save widget
observes those events.
* Created a new event system for all IPython events (events.js).
We should start to use this to allow our classes to be loosely
coupled.
* Created a new notification widget that should be used for all
notifications. Uses new event system.
* Removed the kernel status widget.
* All kernel status message use new event/notification system.
* The print notebook view works again.
