[WIP] Attempt to make extension work with notebook 5.6

[parente]

Notebook 5.6 moved to jQuery 3.x. Gridstack needs an upgrade to work with that version. Jumping to GS 0.4 breaks a lot of stuff. The changes here get things limping along, but drag/drop in layout mode is still broken.

Leaving this here in case someone wants to pick up where I left off. I probably won't be back to it, at least for some time.

[AADeLucia]

I tried to still use Dashboards by downgrading Notebook to 5.5 but that didn't work because Dashboards installs the latest version of Notebook. Can you change which version gets installed with Dashboard? I'm using conda install and I'm on Python 3.7

[parente]

@AADeLucia conda install 'notebook==5.5' dashboards should work. Keep in mind that older versions of notebook may have security flaws, however.

[AADeLucia]

Works, thank you! I had been changing the packages in the wrong order (uninstall/reinstall notebook as 5.5 and then install dashboard) and dashboard kept upgrading my notebook to 5.7. So the following order worked for me:
conda install notebook==5.5
conda install -c conda-forge jupyter_dashboards
jupyter nbextension enable jupyter_dashboards --py --sys-prefix