The robot_trajectory::RobotTrajectory class is basically a wrapper around std::deque<robot_state::RobotStatePtr> waypoints_ and std::deque<double> duration_from_previous_
But (also because this was written long before the C++11 transition), the class does not provide
standard std-container interfaces.

Sometimes it would be rather convenient to use, e.g., for(auto& waypoint : trajectory) or use the class with std-container functions though.

The one challenge here is to decide whether we want to include duration_from_previous_ here (resulting in pairs for iteration).