Using new versioning/version.py file

This replaces the old `kadi/version.py` file with the new-fangled [versioning/version.py](https://github.com/sot/versioning/blob/master/versioning/version.py) that makes the git version info available to the installed package.

This PR also:

- Migrates from distutils to setuptools
- Tidies up `setup.py` a bit

cc: @jeanconn - while you've been doing using operations stuff I was solving this minor problem.