[armature] Add a 'joint trajectory' interface

The new service (armature.trajectory(traj)) allow for execution
of trajectories on an armature: user provide a set of waypoints and
timestamps that the actuator try to follow.

The trajectory structure is similar to ROS' JointTrajectory.

This first version does not support velocities and accelerations, only
positions.

Refer to armature_testing.py for usage examples.
[builder] add Armature class
[ros] topic name w/new object renaming policy
[test] ros laserscan create arc manually
[test] camera flush the socket
[builder] simplify MORSE_DATASTREAM_DICT

Remove MORSE_DATASTREAM_MODULE from MORSE_DATASTREAM_DICT,
set it in AbstractComponent.configure_mw, where we must have mw argument.

See #145 & #217
[builder] replace configure_mw by add_stream