Add widget view options in creating child views
Make the widget keys property traverse the superclasses and accumulate the _keys attributes.

This caches the result, overwriting the property.
Merge remote-tracking branch 'jdfreder/widget-msg' into backbone-flat

Conflicts:
	IPython/html/static/notebook/js/widgetmanager.js
	IPython/html/static/notebook/js/widgets/base.js
Get rid of keys magic; make the keys very explicit
Make widget keys have more explicit inheritance
Merge pull request #8 from jasongrout/backbone-flat

options on child views and automatically accumulating _keys from superclasses