Refactored the tutorial notebook "Reproduce: Stabalizing Feedback Controls for quantum systems" for qutip version 4.6.2

[rupayan2029]

I am new to qutip and want to contribute to the project. I have opened this issue to discuss the refactoring of the notebook titled "Reproduce: Stabalizing Feedback Controls for quantum systems" written by Robert Johansson to work with qutip version 4.6.2. The same issue is raised here in the google group as well. I have made changes to the code cells of the notebook and it seems to me to be working well. Kindly review it and finally guide me on how to add this tutorial to this repository as do not want to violate any rules here unwittingly.

PS: Below is the .md version of the notebook. Reproduce_ Stabilizing Feedback Controls for quantum systems.md