Make Toolbar pip Installable

[psychemedia]

If this package is being distributed as a standalone extension instead of (or as well as) part of jupyter_contrib_nbextensions, it would be useful if it were pip installable, eg as per the RISE or nbdime extensions.

This would also allow the toolbar to be installed "for free" into a MyBinder environment created from the repository.

[joshuazeltser]

It definitely makes sense to do this. I will hopefully add this installation method over the next few days

[psychemedia]

@joshuazeltser Just for completeness, I note here that a notebook extension pip installer can be configured to automatically install and enable the extension: https://jupyter-notebook.readthedocs.io/en/stable/examples/Notebook/Distributing%20Jupyter%20Extensions%20as%20Python%20Packages.html

[jeffyjefflabs]

I see a version on PyPI but it looks like maybe it's an older version of the code? Some of the modules included here have an extra /accessibility_toolbar in the path that makes them fail to load.