Merge pull request #10 from pal-robotics/split-msgs

Split package into play_motion and play_motion_msgs
Use existing msg types for traj points. Refs #4.

- Move from the custom structs to trajectory_msgs types.

- Waypoints can now have accelerations.
Refactor populateVelocities. Document it.
First prototype of motion planning support.

- Add dependencies on MoveIt!
- Add helper class that plans an approach trajectory when needed, and is able to
  reason about which planning groups to use
- Pending tasks documented as inline TODOs
Merge branch 'motion_planning' of https://github.com/pal-robotics/play_motion into motion_planning
Remove log statement of little use.