Porting to python3 - ROS Noetic

[ilyasmg]

The current code has some python2 dependency problems that are not easy to fix and not worth as python2 is deprecated.
I created a new branch ros-noetic with a docker environment to do the porting...currently I'm having some issues with building darknet_ros with opencv4.
If someone is able to build darknet_ros with opencv4 (then maybe it would be good to add the darknet_ros working as a submodule), next step would be to port track.py and track_deep.py to python3, saving dependencies in a requirements.txt so it will be easier to use in the future.
I added the sort and deep_sort packages as submodule in ros-noetic branch (they are both python3 compatible)