Raises Not Implemented Error: Creating rigid body via API

[NicolasKuske]

Function create_rigid_body() to be found in rigidbody.pyx.
In motive version 1.8 this rigidbody would not be trackable by Motive
after it got created. Test that for new Motive version.
Update documentation if new information.

[nickdelgrosso]

Works:

• Creating rigid body in api
• Tracking api-created rigid body in gui

Not yet checked:

• Tracking api-created rigid body in api