Making circuitscape a python package

This will convert `circuitscape` to a python package, that can be registered at `pypi` and installed with `pip`.

Please do not merge this yet.

Though the packaged version of `circuitscape` works fine as a regular python package, I am not able to get it to work as a mac app bundle. I shall try to find out a fix. In the meantime, please give this a try on your machine.