Use a code formatter

I'd like to try out using a the amvb/black code formatter. For those unfamiliar there is a right up here.

The long and short of it is that we add an additional check on code formatting to the CI - essentially a program takes over all formatting options. This is advantages as it reduces the amount of style/syntax differences between difference parts of the code and will makes code review easier as there will never be any style questions.

There are 3 ways to interact with it

1. For casual developers, they can just submit the code as-is, it will fail on 'code formatting and one of us can just run it through the program before it is merged.
2. Anyone can easily pip install black, then just run black FILENAME.py to format and commit (ensuring it passes the CI).
3. In a few lines you can add a pre-commit hook which will automatically "blacken" the code before it is committed.

@isobel.romero-shaw @colm.talbot @charlie.hoy (+ anyone else) what are peoples thoughts?