Add support to load notebooks from URL or from local file

[louisabraham]

You can test locally with:

jekyll serve --baseurl='/iocamljs'

[louisabraham]

My modifications might trigger problems:
- the original code is made to work with a notebook_id and not an URL or a file
- I call load_notebook_success so this.start_kernel();, maybe there is a memory leak, maybe there should be a boolean to call restart_kernel instead
- IPython.Kernel.start takes a notebook_id argument.

[louisabraham]

Hi, did you look at this PR?