Joint Trajectory Action Server Improvements

Splines! Adds linear, cubic and quintic spline segment generation. Adds 'position' control mode switching. Allows for direct position commands to JCBs. Accurate trajectory tracking.
Adds clean control mode switching on exit.
Adds new dynamic reconfig param file for position jtas controller.
Adds parameter overrides from trajectory action requests. Execution trajectory tracking, goal, goal time tolerances take priority when provided in action request.
Adds cuff interaction monitored control mode switching. Exits back to standard joint position control mode when cuff pressed.
Updates per review #22

Adds execution goal velocity constraint.
Merge pull request #22 from RethinkRobotics/joint_trajectory_action_improvements

Joint Trajectory Action Server Improvements