Merge branch example/lqt nullspace on master

Hi Hakan,

Thanks for your contribution on RCFS, before definitely adding your example on the master branch there are some small things to fix:

1. Fix the header of your example, author names, description of your example.
2. Use an object to store your example's parameters (see: https://gitlab.idiap.ch/rli/robotics-codes-from-scratch/-/blob/master/python/iLQR_manipulator.py#L88 )
3. Put all your functions on top of the file (like in https://gitlab.idiap.ch/rli/robotics-codes-from-scratch/-/blob/master/python/iLQR_manipulator.py )

Thanks!

Have a nice day, Jérémy