Added support for Python 3

[Jakubach]

Some functions (PyInt_AsLong and PyString_FromString) used in Python 2 are deprecated in Python 3. This changes are needed if you would like to build your project with Python3 support.

[Jakubach]

When building I found also a problem with rviz_visual_tools package. It does not found method: clearAllTransforms from tf_visual_tools.h
I solved this by installing rviz_visual_tools package from source

[JStech]

Thanks! We should definitely support Python 3, so this is very useful.

[JStech]

I've not tested this, but it looks good. Side note: maybe we should discuss what ROS version we're targeting. (I'd vote Noetic, since Ubuntu 20.04 comes with OpenCV 4.2.)

[tylerjw]

These changes look good to me, I second targeting a Noetic release of this package. @JStech maybe you can help me by leading releasing moreit_calibration with the reset of the moveit packages this cycle. Here is a link to the instructions.

The specific tests you could help compete to shepherd this being released are:

1. Create the release issue
2. Update changelogs
3. Prepare announcements
4. Test moveit_calibration on Ubuntu 20.04 with Noetic

I am happy to do the bloom steps.

[JStech]

I did finally get a 20.04 installation up and running, and I was able to test this in Noetic and Python 3. There were two other things I had to do to get it all to work, but this change was sufficient within the repo.

Besides this change, I also:

• Downloaded and built the baldor package, which is not released to Noetic
• Downloaded and built the handeye package, with a small modification to make it Python 3 compatible

So yeah, no changes requested for this PR. This felt like the right place to document what it takes to run in Python 3.

[mfkenson]

My course project team is working on the hand eye calibration on noetic today and rviz kept complaining solver can’t return result until we followed what @JStech suggested.

[JStech]

The CRI Group packages, baldor and handeye, have now been released for noetic, so you can just apt install ros-noetic-handeye ros-noetic-baldor (or use rosdep install) and you're good to go. Hopefully soon you'll also be able to apt install ros-noetic-moveit-calibration