* Hash-deduplicated state storage (and migrations) for PostgreSQL and SQLite
* Refactor droomserver database setup for migrations
* Fix conflict statements
* Update migration names
* Set a boundary for old to new block/snapshot IDs so we don't rewrite them more than once accidentally
* Create sequence if not exists
* Fix boundary queries
* Fix boundary queries
* Use Query
* Break out queries a bit
* More sequence tweaks
* Query parameters are not playing the game
* Injection escaping may not work for CREATE SEQUENCE after all
* Fix snapshot sequence name
* Use boundaried IDs in SQLite too
* Use IFNULL for SQLite
* Use COALESCE in PostgreSQL
* Review comments @Kegsay
* 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
* Emit redacted_event from the roomserver when redactions are validated
- Consume them in the currentstateserver and act accordingly.
- Add integration test for the roomserver to check that injecting
`m.room.redaction` events result in `redacted_event` being emitted.
* Linting
* Ignore events that redact themselves
* Implement core redaction logic
- Add a new `redactions_table.go` which tracks the mapping of
the redaction event ID and the redacted event ID
- Mark redactions as 'validated' when we have both events.
- When redactions are validated, add `unsigned.redacted_because`
and modify the `eventJSON` accordingly.
Note: We currently do NOT redact the event content - it's gated
behind a feature flag - until we have tested redactions a bit more.
* Linting
