Flake8 non-formatting changes

[bajnokk]

This PR contains a series of patches to resolve flake8 violations, which are not just code formatting. The ignored violations are appended to tox.ini, so now flake8 --config tox.ini should pass without an error.

This patch series depends on #422 , so that one can run the unittests on a standard development environment.

All Submissions:

• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Have you added an explanation of what problem you are trying to solve with this PR?
• [x] Have you added information on what your changes do and why you chose this as your solution?
• [ ] Have you written new tests for your changes?
• [x] Does your submission pass tests?
• [x] This project follows PEP8 style guide. Have you run your code against the 'flake8' linter?

[c00kiemon5ter]

Thank you! Some of those conventions may change, as I think they are in conflict with pysaml2's ruleset and conventions (which will probably be shared with this project). But for now this is an improvement ;)