Feature Request: Best Particle Pose

[tridivb]

Hi,

Thank you for the source code. Recently I was working on something where I needed the 2D coordinates of the bot inside the map. I tried doing it by using the the odom transformation published by gmap but the visualization showed that it was not always correct. Therefore, I used the best particle pose and published it as the PoseStamped message. The pose visualization showed this to be more accurate than the previous one. If it is something that you think will be helpful, I will create a pull request for the same.