Add crystal toolkit and pymatviz

[janosh]

• https://github.com/materialsproject/crystaltoolkit
• https://github.com/janosh/pymatviz

Disclosure: I'm the maintainer of pymatviz and contributor to crystaltoolkit.

[janosh]

@mkhorton Let me know if you'd like me to make any changes to the crystaltoolkit entry.

[blokhin]

@janosh many thanks :+1: :+1: :+1: