Automatic code formatting

We want something like gofmt for python. We want to minimize changes to existing code while defining a style we agree to. Ideally it should automatically format files on save (PyCharm integration would be great) and/or as a precommit hook.

One option: https://github.com/google/yapf

From @eukreign on Slack: but to elegantly switch to yapf would require:

1. defining a new config that's as close to current code as reasonable
2. running the converter and adding a comment to any datastructure that is uglified by yapf

whoever takes on this project should be willing to carefully skim through the changes yapf makes to make sure it's not uglier (at least not too much uglier) than before