(Rebase) Inverse Dynamics Feed Forward

This branch is a rebase of for the Inverse Dynamics pull request since it was based off master. See PR #46 for a full discussion.

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