Change tabs to spaces

[whot]

this is going to mess up the history a bit, but it's better to do it earlier than later. Spaces are preferred, with 4 spaces per indent.

https://www.python.org/dev/peps/pep-0008/#tabs-or-spaces

I think it's worth just running a script over the repo to fix this once and for all and be done with it.

That's the main flake8 complaint right now, so let's get that out of the way first.