Investigate/implement packaging of OpenRVDAS in pyproject.toml

Configuring OpenRVDAS as a "python project" as administered by the new standard packaging system will allow simplifying installation (takes care of requirements.txt) and code (will obviate need for all those sys.path.append(...) lines.

https://realpython.com/python-pyproject-toml/

https://packaging.python.org/en/latest/guides/writing-pyproject-toml/

