Add QuTiP Lectures to the repository

[christian512]

I have added all notebooks from the qutip-lectures repository to this repository. This includes:

• Updating the header description of the notebook
• Update broken links
• fix all python code to work with current release of qutip
• add the notebooks to the test pipeline

The contents of the notebooks are not changed.

[hodgestar]

Whoops. GitHub Actions seems to still be a little slow to start today after the outage yesterday so I accidentally merged before the build started.