Added a new ROS publisher for DepthVideoCamera

DepthVideoCamera used VideoCameraPublisher to publish the depth images in ROS. Those had the encoding in the ROS message set to `rgba` then. This is not what ROS assumes which is 32FC1. The actual data are in that format already, so the only change required was to set the right encoding. Since that would collide with the rgb image publishing, a new publisher is needed.