Migration of vdom Jupyter extension under nteract

[dlqqq]

vdom currently has some incompatibilities with JupyterLab that are forcing us to remove it from the core distribution. Given that vdom has not been maintained for 3+ years, we think that the best way of doing so would be to first migrate the vdom Jupyter extension packages underneath the nteract org umbrella. That way, if vdom ever gets revived again, the vdom extension packages can also be easily revived. Without this migration, users who wish to fork/contribute would be forced to dig through the old JupyterLab git history to extract the extension source code.

A few questions:

1. Are there any objections to this proposed migration?
2. Can we get consensus on a repository name? I was thinking nteract/vdom-extension.

[rgbkrk]

I noticed this error recently with an IPython upgrade which motivated me to bring this package up to date.