I added the ramp_msgs package to hold all of the messages. We can't use the JointTrajectory msg because it gives us no information about knot points.
The Trajectory msg is simply a JointTrajectory and a uint16[] that holds the indices of the knot points in the JointTrajectory.
The Path msg is the list of configurations in a path. The Path msg will be passed to the trajectory_generator package by the planner to get trajectories.