Inverse Dynamics FeedForward

The Inverse Dynamics Feed Forward update to Baxter's Joint Trajectory Action Server (JTAS) is meant to 

- Create smoother interpolated paths between trajectory points that are passed into the server by using Bezier curves. These curves keep the interpolated trajectory continuous in 3 dimensions (position, velocity, acceleration) for each joint
- Allow faster movements when using JTAS by feeding forward the trajectory's velocities and accelerations commands into the motor controller
- Maintain compatibility with trajectories that supply position-only trajectory points
JointTrajectoryPoint is the message type of the inverse_dynamics_command publisher @line 122