General improvements

 * Messages added to their own `edu.wpi.rail.jrosbridge.messages` package [(rctoris)](https://github.com/rctoris/)
 * `geometry_msgs` added to the `edu.wpi.rail.jrosbridge.messages.geometry` package [(rctoris)](https://github.com/rctoris/)
 * Services added to their own `edu.wpi.rail.jrosbridge.services` package [(rctoris)](https://github.com/rctoris/)
 * JUnit test cases added [(rctoris)](https://github.com/rctoris/)