Hemisphere Joint IK

Closes #62 (closed)

With @klas and @meixner

Contains !120 (merged) => See !122 (closed)

ToDo:

• Cleanup

Content:

• Compute orientational part of Jacobian for hemisphere joint in maths
• Set Jacobian of hemisphere joint in Differential IK
• Fix CompositeDiffIK crashing when there is no nullspace (less DoF than workspace)
• Refactor hemisphere joint node