Online robot joint_state subscriber has no indication it fails

[geoffreychiou]

For online planning, the OnlineRobot object relies on a joint_state subscriber to inform itself on the current position of the robot and give the first point of a trajectory. If for some reason nothing is publishing on that topic, it will default to zeros.

This can lead to dangerous scenarios (such as on a ur10) where the robot shoots straight out instead of starting the trajectory at its current position.

We should add a check for messages with a timeout and throw and exception if nothing is received to prevent motion plans from being executed.