Move to conda-forge noarch package

[jasongrout]

If we haven't moved to a noarch package on conda-forge yet, we should complete the migration by 8.0.

See conda-forge/widgetsnbextension-feedstock#52

[jasongrout]

I did this in the prerelease widgetsnbextension package: conda-forge/widgetsnbextension-feedstock#58. Leaving this open until the main package moves to noarch, though.

[mwcraig]

ipywidgets has been done, see https://github.com/conda-forge/ipywidgets-feedstock/blob/master/recipe/meta.yaml#L13 but widgetsnbextension has not been done yet on the main branch https://github.com/conda-forge/widgetsnbextension-feedstock/blob/master/recipe/meta.yaml#L11

[davidbrochart]

I opened conda-forge/widgetsnbextension-feedstock#65.

[jasongrout]

This is currently done in the prerelease conda-forge package, so should Just Work when we release the next major version.