Add back `jupyter nbextension` commands as an alias to `jupyter labextension`?

### Problem

For some users it might be odd to type the `jupyter labextension` commands if they only use Jupyter Notebook 7 and not JupyterLab.

### Proposed Solution

Maybe it could make sense to add some of the `jupyter nbextension` commands back to Notebook 7, which would just be an alias for `jupyter labextension`? For example:

- `jupyter nbextension list` -> `jupyter labextension list`
- `jupyter nbextension enable` -> `jupyter labextension enable`
- `jupyter nbextension disable` -> `jupyter labextension disable`

There might also be some pros for keeping the `jupyter labextension` command, to explicitly indicate Notebook 7 extensions are JupyterLab extensions.

Although the extensions would still be located under `PREFIX/share/labextensions`.

### Additional context

No strong opinions to add it back. Opening the issue to see if users and / or maintainers would think this could be useful.

Start by tracing the existing `jupyter labextension` entry point and the historical `jupyter nbextension` commands named in the issue. Determine the scope and compatibility of aliases for `list`, `enable`, and `disable`; done means the agreed aliases behave consistently with their corresponding labextension commands.

Written by the indexing model from the issue text.