During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
Refactoring to pass the device ID (in addition to the user ID) through
the presence handler (specifically the `user_syncing`, `set_state`,
and `bump_presence_active_time` methods and their replication
versions).
This adds support for the stable identifiers of MSC2285 while
continuing to support the unstable identifiers behind the configuration
flag. These will be removed in a future version.
* Changes hidden read receipts to be a separate receipt type
(instead of a field on `m.read`).
* Updates the `/receipts` endpoint to accept `m.fully_read`.
