During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
Implements stable support for MSC3882; this involves updating Synapse's support to
match the MSC / the spec says.
Continue to support the unstable version to allow clients to transition.
Dangerous actions means deactivating an account, modifying an account
password, or adding a 3PID.
Other actions (deleting devices, uploading keys) can re-use the same UI
auth session if ui_auth.session_timeout is configured.
Part of #9744
Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.
`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>`
- Update black version to the latest
- Run black auto formatting over the codebase
- Run autoformatting according to [`docs/code_style.md
`](80d6dc9783/docs/code_style.md)
- Update `code_style.md` docs around installing black to use the correct version
