* Simplify send-to-device messaging
* Don't return error if there's no work to do
* Remove SQLite migrations for now
* Tweak Postgres migrations
* Tweaks
* Fixes
* Cleanup separately
* Fix SQLite migration
* Give read recipts their own database sequence
* Give receipts their own stream ID
* Change migration names
* Reset sequences
* Add max receipt queries, missing stream_id table entry for SQLite