Style fixes: wrap long lines, fix hanging indents, bump flake8

### Changelog:
* Wrap *most* long lines (`E501`) in *most* python files.
* Fix all bad hanging indents (`E127`). Enable relevant build check.
* Bump version of `flake8`. New version supports multithreading, so `make style` will be a little bit faster.
I didn't write this but I think it's so a specific browser tag can't be blocked or to prevent caching.