During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.

* Clarifies comments and documentation.
* Adds type-hints.
* Fixes Python 3 compatibility (and runs pyupgrade).
* Updates for changes in Synapse internals.

Run `isort`, `flake8` and `black` over the `contrib/` directory and `synctl` script. The latter was already being done in CI, but now the linting script does it too.

Fixes https://github.com/matrix-org/synapse/issues/7910

* Fix seven contrib files with Python syntax errors

Signed-off-by: cclauss <cclauss@me.com>

Signed-off-by: Adrian Tschira <nota@notafile.com>