Reformat all files with the new version.

Signed-off-by: Marcus Hoffmann <bubu@bubu1.eu>

 - Update black version to the latest
 - Run black auto formatting over the codebase
    - Run autoformatting according to [`docs/code_style.md
`](https://github.com/matrix-org/synapse/blob/80d6dc9783aa80886a133756028984dbf8920168/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

fix the copyright holder from matrix.org to OpenMarket Ltd, as matrix.org hasn't been incorporated in time for launch.

add in copyrights to everything, not just the synapse subdir, and add a copyrighter.pl whilst we're at it