Update to JupyterLab 2.0

[jtpio]

Fixes jupyterlab/jupyterlab#8208

Update to JupyterLab 2.0 and bump a few other widget dependencies.

To test this PR on Binder:

[blink1073]

Do you mind trying to upgrade miniconda to python 3.7 to fix the appveyor issue?

[jtpio]

Done, let's see how it goes.

[jtpio]

Now the error seems to be caused by xeus-cling that can't be installed on Windows.

It looks like this has already been discussed in #81

[blink1073]

I'd say let's drop appveyor.yml, there's no urgent need for the demo to be built on Windows.

[jtpio]

That sounds reasonable. For reference this was also the case when updating to JupyterLab 1.0: #91

I'll remove appveyor and trigger another Binder build.

[blink1073]

Appveyor failure is expected until we merge this. The Travis failure seemed like a connectivity issue, kicked it.

[blink1073]

Thanks @jtpio!

[saulshanabrook]

@jtpio i think the error is because the version of jupyterlab_server is too old in binder. It needs to be at least 1.1.0: jupyterlab/jupyterlab#8127 and it's 1.0.6.

I am not sure why it's pulling in an old version.

[jtpio]

This should fix it: conda-forge/jupyterlab-feedstock#213

[jtpio]

To add more context, the issue mentioned here is this one: jupyterlab/jupyterlab#8231