Transition to JupyterLab 2.0.0

[consideRatio]

JupyterLab 2.0.0 is out, and this extension have conflicting dependencies with its core packages. This PR is me following the JupyterLab migration guide referenced below, as I have now done for many other repositories successfully.

PR Summary

1. I bump the version of this npm package to 0.2.0 from 0.1.6 in package.json.
2. I bump the @jupyterlab/... dependencies one major version.
3. I replace @phosphor with @Lumino.
4. I updated this extension to align with practices from the cookiecutter template used to generate the repo initially, this was done in the final commit 1f9c504.
5. Releasing this will not break existing use of JupyterLab 1, but they will stay behind if new features are added, and the new features will only be available in JupyterLab 2.

References

• Change log for developers
• A migration guide

[MichaelJiangPlus]

Although the new version of the dependency cannot be directly applied to jupyterlab 1.0 after updating, it is very effective for jupyterlab 2.0

[zhytang]

I think you can delete package-lock.json and update tsconfig.json like this

[consideRatio]

@zhytang ah that would make everything more in line with the current cookiecutter template to create a jupyterlab extension, but I didn't see package-lock.json be in the .gitignore, so I think the cookiecutter is opinionated towards including it.

https://github.com/jupyterlab/extension-cookiecutter-ts/tree/master/%7B%7Bcookiecutter.extension_name%7D%7D

[zhytang]

when NPM is used to publish packages, package-lock.json will not be published, so I think we can add it to the .gitignore.
It's just a suggestion

[consideRatio]

@zhytang i updated this extension based on the jupyterlab extensions cookiecutter repo: https://github.com/jupyterlab/extension-cookiecutter-ts

I didn't remove package-lock.json as it would go against the typical practice I've seen across many other jupyterlab extensions as well as this repo.

[consideRatio]

@chaoleili if you have time, this is ready for review/merge I'd say!

[chesterli29]

@chaoleili if you have time, this is ready for review/merge I'd say!

Thanks a lot for your contribution! 🎉