add utility function to read nested ros parameter vector to jsk_topic_tools

add new utitlity function to jsk_topic_tools

```c++
  bool readVectorParameter(
    ros::NodeHandle& nh,
    const std::string& param_name,
    std::vector<std::vector<double> >& result);
  bool readVectorParameter(
    ros::NodeHandle& nh,
    const std::string& param_name,
    std::vector<std::vector<std::string> >& result);
```