Fix coding style

OCD alert.

I fixed some of the most obvious PEP8 issues in python files, with pycodestyle.
There are still quite a few > 79 chars that somebody else can take care of if they want, I wasn't really sure if/how to tackle them.

Also unified indentation in templates.

And the shebang to python3, to prevent the world from falling apart :)

I can split this in multiple MRs if needed.