Make configurable file/directory bindings

[vmenger]

It would be nice to be able to mount local directories to the docker image so that files can be used in the notebook.

I could see it work:

• As a parameter to the docker install command e.g. dockernell install image_1 --bind c:/data /opt/data/ ~/.aws ~/.aws
• In an optional config file stored in ~/.dockernel (e.g. a json file with {"name": "image_1", "bindings" : {"C:/data": "/opt/data/", "~/.aws": "~/.aws"}})

Second one would be especially useful for mounting config files like .aws or pip.ini in some docker kernel. Nice addition moreover would be to add the option to mount to all dockernel installs.

[MrMino]

Both points seem to be great ideas. I'll probably do this in the upcoming weeks, but if you'd like to do it, notify me - PRs welcome!