Various maintenance fixes

[jdiez17]

Hey there, thank you for making these tools! I have managed to get them up and running, but I had to make some tweaks to get there. I'm running ROS Noetic, Python 3.9 on Arch Linux.

1. I changed some of the import statements to allow Python 3 to locate the modules correctly.
2. I changed two values in the aruco_analyzer_node.launch script. I'm a n00b at ROS so I could be wrong, but:
   2.1. it seems to me that the camera_ns is supposed to be /cameras instead of /sensors, since most of the camera bringup launch scripts use that as the topic prefix.
   2.2. using the latest image/camera drivers for ROS it seems the /color/image_raw transport hint has somehow changed, and it is now supposed to be just /image_raw.
3. It looks like there was a change to cv2 that requires us to pass the rvec and tvec vectors as arguments to cv2.aruco.estimatePoseBoard. Those are used as initial guesses.