Add an example to show model updates in the web version.

This required us to pull the tornado ioloop initialization out of the jigna
view. This is in conjunction with the analogous behavior in Qt where we start
the application event loop outside of the jigna view.
Minor renaming.
Trying to make the QtServer quack like a regular webserver.
Minor cleanup.
View.show() now returns the `widget` object.

This allows one to perform layout operations on the widget.control
object which is a native QWidget. Note that this api is conformant
with traitsui API where they return the `ui` object on calling
`edit_traits`.
Add the ability to specify size to a jigna view.
Clean up View api: `create_widget`, `create_webapp` instead of show/serve.

Also got rid of the `update_context` method on the view.
Pull out application.listen from the `server`.

Also renamed the `serve` method of the server to an initialize method.
Create the HTMLWidget on the server.
Add a super basic example to show embedding of jigna widget to Qt.

The example needs some cleanup though.
Clean up the embedding in Qt example.
Minor cleanup.
Respect the parent attribute of the `create_widget` method.
Minor cleanup.
Minor renaming
Minor cleanup.
Minor: Rename `size` trait of the View to `default_size`.
Add the warning regarding `async` trait in case of full HTML.
Minor commenting cleanup.
Minor change in the commenting style of simple_view example.