Solving #5997: instances of WidgetView (that are not instances of DOMWidgetView) do not trigger widget_area.show anymore.
Merge pull request #6115 from SylvainCorlay/widget-area-show

Instances of WidgetView do not trigger widget_area.show anymore.
Changes outputarea to an iframe

Modifies outputarea so that most of the logic of this class is done inside an iframe.  This code will need a lot of cleanup, but it provides the basic framework for separating outputarea functionality into an iframe.
Start moving code back into notebook dir.
	renamed:    outputframe/js/outputarea.js -> notebook/js/outputarea.js
Started getting widgets to work in iframes
Making some progress...