The TCP replication protocol streams deltas of who has started or
stopped syncing. This is different from the HTTP API which periodically
sends the full list of users who are syncing. This commit adds support
for the new TCP style of sending deltas.

This defines the low level TCP replication protocol

The new replication protocol will keep all the streams separate, rather
than muxing multiple streams into one.

Fix bug where current_state_events renamed to current_state_ids

* Bail early if remote wouldn't be retried

* Don't always return true

* Just use get_retry_limiter

* Spelling

Don't user upsert to persist new one time keys

Notify on new federation traffic

Fix installation issues

Batch sending of device list pokes

Short circuit if all new events have same state group

Use presence replication stream to invalidate cache

Add slave transaction store to workers who send federation requests

Instead of using the cache invalidation replication stream to invalidate
the _get_presence_cache, we can instead rely on the presence replication
stream. This reduces the amount of replication traffic considerably.

Cache hosts in room

try not to drop context after federation requests

Add another missing yield on check_device_registered

Reduce some CPU work on DB threads