Fix ShellInABox to use iFrame

[ptone]

Currently works pretty well, main limitation is that it does not display the 'login:' prompt, as it is getting drawn off screen.

Can "fix" in the dev-browser by switching JS console context to the iFrame, and calling "new ShellInABox();"

which triggers the refresh - this is the call that originally generates the shellinabox UI - but this technique can't be used from parent page to iFrame outside the dev console context due to browser security policies (shellinabox is served on a different port).