Fix mechanicalproperties.py. Synchronize mechanicalproperties.py from Matlab.

[inwoo-park]

CHG: Matlab > Python, Synchronize mechanicalproperties.py

[TidbitSoftware]

By the way, @inwoo-park I've added you to the contributors group so you no longer have to submit pull requests, you can now commit directly with git push. Of course, if you like the workflow of having your own fork, you can continue to do that.

[inwoo-park]

Hi @TidbitSoftware ,

Thank you for inviting contributor group in ISSM.

To maintain the stable ISSM, I will make a separate branch and do a pull request.

Best regards,
Inwoo