Add setup.py to allow for pip installation

Minimal setup.py enables installation as a Python package using pip, e.g. pip install . from within the directory.

Could also be used directly from the git repository, for example in setup.py:

setup(
    install_requires=[
        "ibisclient @ git+https://gitlab.developers.cam.ac.uk/uis/sysdev/devgroup/ibis/ibis-client.git"
    ]
...
)