Set link padding

this is patch for https://github.com/ros-planning/moveit_ros/issues/402, add following 4 values

```
  /// default robot link padding                                                                                                                        
  std::map<std::string, double>         default_robot_link_padd_;
  /// default robot link scale                                                                                                                          
  std::map<std::string, double>         default_robot_link_scale_;
  /// default unpadded robot link padding                                                                                                               
  std::map<std::string, double>         default_robot_link_unpadded_padd_;
  /// default unpadded robot link scale                                                                                                                 
  std::map<std::string, double>         default_robot_link_unpadded_scale_;
```

please check #341, it explains the reason we need unpadded robot.