Fix labextension install path

[toslunar]

Fix #131.

Fix shared-data config to align with dest in _jupyter_labextension_paths.

Fixing dest instead doesn't work. Maybe it's an issue of ipywidgets or jupyterlab, because
https://jupyterlab.readthedocs.io/en/latest/extension/extension_dev.html#distributing-prebuilt-extensions says "typically", not "exactly"

To distribute a prebuilt extension, copy its output directory to a location where JupyterLab will find it, typically <sys-prefix>/share/jupyter/labextensions/<package-name>

[martinRenou]

LGTM!