Handle sensor_id via roslaunch arg/param and set_sensor_id service

[sven-hoek]

I wrote a patch to make the radar use a configurable sensor_id, which can be set via roslaunch arg.

This also makes it possible to use the radar without problems after calling the set_sensor_id service without restarting the node as it updates the current sensor id and starts looking for the correct message IDs after a change. After a restart of the node, the roslaunch arg/param has to be set to the new sensor_id, of course.

Also included is a converter from object lists to ROS radardetection messages. Haven't yet added the function to convert from cluster lists but might do.