EXAMPLES: tweaks to boilerplate
BUG: don't ignore height param in UrlDisplay
ENH: make UrlDisplay smarter

- each IFrame get a UUID id
- add support for exchanging messages between IFrame
and IPython window.
- if we're in IPython inline an a handler that tells the IFrame in which
cell it's living, and implment code for accepting a blob, overwriting the
Output area and the DOM with it, so that the frozen view bceomes
visible, and is serialized with the notebook. NBviewer support.
CLN: dead code in examples