* Offset updates take place using TransactionWriter
* Refactor TransactionWriter in current state server
* Refactor TransactionWriter in federation sender
* Refactor TransactionWriter in key server
* Refactor TransactionWriter in media API
* Refactor TransactionWriter in server key API
* Refactor TransactionWriter in sync API
* Refactor TransactionWriter in user API
* Fix deadlocking Sync API tests
* Un-deadlock device database
* Fix appservice API
* Rename TransactionWriters to Writers
* Move writers up a layer in sync API
* Document sqlutil.Writer interface
* Add note to Writer documentation
* Updated TransactionWriters, moved locks in roomserver, various other tweaks
* Fix redaction deadlocks
* Fix lint issue
* Rename SQLiteTransactionWriter to ExclusiveTransactionWriter
* Fix us not sending transactions through in latest events updater
* Persist partition|offset|user_id in the keyserver
Required for a query API which will be used by the syncapi which
will be called when a `/sync` request comes in which will return
a list of user IDs of people who have changed their device keys
between two tokens.
* Add tests and fix maxOffset bug
* s/offset/log_offset/g because 'offset' is a reserved word in postgres