Try using black for code formatting

[alisonrclarke]

• Add pre-commit to enable black in git hooks
• Added pyproject.toml to set up black config
• Re-formatted files

This is just a suggestion to use Black - happy to debate it. Just found we were using a mixture of tabs and spaces (sorry, not sure why I was using tabs) so thought it might be better to have something that formats the code for us on check-in. I'm not entirely convinced by the style black uses, but it will keep things consistent.