Add black as an auto formatter

[arogl]

WIP - Add black as an auto formatter

Follows on from #3694 and the hard work by @jtpavlock

Requires #4030

Checking tests

To Do

• Documentation. (If you've add a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst near the top of the document.)
• Tests. (Encouraged but not strictly required.)

[arogl]

Will rebase on master