Add LinearHolonomicTask

[shbang91]

I closed the old PR and instead made cleaner commit history.

Here, the major changes are the following:

1. Removed the draco3 robot description
2. Added a general class of LinearHolonomicTask
3. Added a child class of LinearHolonomicTask called JointCouplingTask

I am looking forward to seeing any feedback from you.

Thank you!

[stephane-caron]

Thank you for this improvement! The PR is starting to look good. I just have one technical point re. the computation of the error in the base LinearHolonomicTask.

[stephane-caron]

Would you be up for adding unit tests for the new tasks in the tests/ folder?

You could take inspiration from test_posture_task.py to spin e.g. test_linear_holonomic_task.py and test_joint_coupling_task.py.

[shbang91]

Would you be up for adding unit tests for the new tasks in the tests/ folder?

Yes, I can make those unit tests.

[shbang91]

Based on your comments above, I've made some changes and added unit tests. Please feel free to give me any feedback you might have.
By the way, I've tried to edit the documentation, but I don't know exactly how it works, so maybe I need to leave it to you 😥

[stephane-caron]

LGTM. I took care of the documentation, fixed the issue mypy had when verifying the weights matrix, and merged this PR. @shbang91 thank you for your contribution 😃