PyOpenWorm coding standards

Pull requests are required to follow the PEP8 Guidelines for contributions of Python code to PyOpenWorm (with some exceptions). Compliance can be checked with the pep8 tool and these command line arguments:

--max-line-length=120 --ignore=E261,E266,E265,E402,E121,E123,E126,E226,E24,E704

Some violations can be corrected with autopep8.