global: use a static code analysis tool

[jacquerie]

As discussed with @jmartinm, in order to have better reviews we need a better baseline for code quality (otherwise we waste lots of time commenting on obvious stuff like indentation, imports...).

The solution to this is a static code analysis tool. I like prospector, which is a wrapper over several tools, except that critical PRs have been sitting unmerged for months (like prospector-dev/prospector#193).

Another one is flake8, which wraps less tools but looks better maintained overall. It still catches lots of stuff:

% flake8 --count --ignore=E501

[...]

892

IMO we should implement flake8 now and add later pylint, pyroma, vulture... (the rest of the stuff in prospector)

[jacquerie]

Some more options: https://github.com/mre/awesome-static-analysis#python

[kaplun]

@spirosdelviniotis, after you have finished with the merging PRs, this could be an interesting horizontal task. I.e. to go through all the warnings generated by flake8, and help improving the code base, thus making INSPIRE code base overall more robust.

Some gotchas are extremely easy, but some other are more interesting and allow to further improve Python skills.

[jacquerie]

I think we agreed to do this.