Feature Request: Move os.path to newer pathlib calls

[ryanskeith]

pathlib can replace the functionality of os.path. It is a newer interface to all things path and I believe it to have a better and more Pythonic API than os.path.

As we don't have any constraints on Python versions or legacy code, I propose we move to the newer interface internally.

[schuylermartin45]

Tracking: https://anaconda.atlassian.net/browse/PAT-184