This change alleviates a significant pain-point for consumers of Jupyter
Kernel and Enterprise Gateway projects by embedding the few classes defined
in the NB2KG server extension directly into the Notebook server. All code
resides in a separate gateway directory and the 'extension' is enabled
via a new configuration option `--gateway-url`.
Renamed classes from those used in standard NB2KG code so that Notebook
servers using the existing NB2KG extension will still work.
Added test_gateway.py to exercise overridden methods. It does this by
mocking the call that issues requests to the gateway server.
Updated the _Running a notebook server_ topic to include a description
of this feature.
Kevin Bates