Python3 compatibility for noetic

[Timple]

As a start for #51

I've never used the mouse teleop and I don't think that one is easy to verify in dockers.

So we could release this as-is or wait for someone to validate functionality.

[bmagyar]

I've just merged a long-standing PR that caused a minor conflict, could you please rebase and touch that one up?

My question regarding this PR is, whether you think it could actually go into Kinetic/Melodic also? The proposed changes seem compatible but I'm not sure about the package.xml versioning constraints

[Timple]

The reason I choose for the conditions in the package.xml is to keep things backward compatible.

Otherwise we can create a noetic-devel branch without the conditions.

But since all active ROS1 distributions are supported now by the kinetic-devel branch, perhaps rename that one to ros1-devel? But that would not be backwards compatible for people building from source maybe..

edit: and to answer your question, conditions work in kinetic: https://answers.ros.org/question/286969/use-identical-packagexml-for-ros1-and-ros2-pkgs/?answer=287026#post-id-287026