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

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&gt;`>

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