Fix the cell reference in views

This solution is kludgy, but it does fix what broke when we tried to take the cell references out of views.
Conflicts:
	IPython/html/static/notebook/js/widgets/widget.js
make the saving to python a method of the model, called with callbacks

Conflicts:
	IPython/html/static/notebook/js/widgets/widget.js
update example notebooks
Pass the whole message into the widget manager display_view call

We do this so implementations can see metadata and any other things in the message, if they want.
Conflicts:
	IPython/html/static/notebook/js/widgetmanager.js
Delete unnecessary save
Cherry pick of @jasongrout 's 2bc2f96.

Only merged changes to notebook and kernel...  (see original comment below).

Separate the widget registry from the widget managers;
attach widget managers to kernels.

Yet to do: take care of clean-up when a kernel is deleted
Conflicts:
	IPython/html/static/notebook/js/widgetmanager.js
	IPython/html/static/notebook/js/widgets/widget.js