Add CRTK/Python based teleop example

[adeguet1]

Many users are trying to implement their own teleoperation and deriving the existing C++ component is not trivial (C++/CMake/package.xml). Python over ROS will add some latency but it would be a lot easier for users to get started. It should include:

• use dVRK events for user present/clutch
• align MTM
• position based unidirectional teleop (same logic as C++ code)
• translation scale
  Not initially required:
• registration for change of coordinate systems
• proxy for gripper/jaws