Panel-chemistry

Added guicolor and improved reference notebook of JSME Editor

https://user-images.githubusercontent.com/42288570/119439642-13e1c400-bd23-11eb-8ad3-7826a030c771.mp4

In this release

- a first version of the `JSMEEditor` is included.
- We created a draft of a nice reference notebook.
- we released the first `panel-chemistry` package to Pypi. Check out https://pypi.org/project/panel-chemistry/
- We improved the look and feel of the project


This release add a JSME Editor Widget. But only as a dummy widget.

The idea is to demonstrate that the easiest way to add a new Bokeh/ Panel extension is to start as simple as possible. And that is to copy some existing small component, refactor minimally, build and test it works. Then you can start refactoring and extending the component.


You can see how this was implemented in this video https://youtu.be/AA8qIY_zrbA

Supplementary written documentation can be found in

- [Bokeh - Extending Bokeh](https://docs.bokeh.org/en/latest/docs/user_guide/extensions.html)
- [Awesome Panel - Bokeh Extensions](https://awesome-panel.readthedocs.io/en/latest/guides/awesome-panel-extensions-guide/bokeh-extensions.html)

Have run `bokeh init --interactive` as described in

- [Extending Bokeh](https://docs.bokeh.org/en/latest/docs/user_guide/extensions.html#pre-built-extensions)
- [Awesome Panel - Bokeh Extensions](https://awesome-panel.readthedocs.io/en/latest/guides/awesome-panel-extensions-guide/bokeh-extensions.html#steps-for-the-awesome-panel-extensions-package-as-of-20200721-panel-0-9-7-bokeh-2-1-1)

and aligned `package.json` and `tsconfig.json` with the same files in the Panel project.

You can see how this was done here https://www.youtube.com/watch?v=6XVEIiP52UU

This Release provides the basic structure of a HoloViz Panel Extensions project. This includes

- A nice CLI based on [Python Invoke](http://www.pyinvoke.org/)
- Automated tests on pull requests and pushes to the `main` branch based on Github Actions.
- A nice setup for [Binder](https://mybinder.org/) including example notebooks, panel apps served and VS Code server.
- A nice `setup.py` file for release to PyPi.