Add images used in the ROS wiki doc.
Add basic description in package.xml.
Rename hold_trajectory_duration

- hold_trajectory_duration -> stop_trajectory_duration for more clarity.

- During Hydro, hold_trajectory_duration will still work, giving a deprecation
  warning.
Merge branch 'hydro-devel' of https://github.com/willowgarage/ros_controllers into hydro-devel