* 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
* Move Updater structs to shared and use it for postgres
* Add constructors for NewXXXUpdater and a useTxns flag
In sqlite, we set useTxns=false and comment why.
* Handle nil txn
* Handle nil in transaction
* Missed one
* Close the txn at the right time
* Don't close the transaction as we reuse it between calls
