Implement purge_history by timestamp

Remove ability for AS users to call /events and /sync

Split Directory store

This functionality has been deprecated for a while as well as being
broken for a while. Instead of fixing it lets just remove it entirely.

See: https://github.com/matrix-org/matrix-doc/issues/1144

Test and fix find_first_stream_ordering_after_ts

It seemed to suffer from a bunch of off-by-one errors.

Expose this as a public function which can be called outside a txn

Fix bug with delayed cache invalidation stream

Split registration store

We poked the notifier before updated the current token for the cache
invalidation stream. This mean that sometimes the update wouldn't be
sent until the next time a cache was invalidated.

Add missing yield during 3pid signature checks

 Fix typo in getting replication account data processing

Split out SignatureStore and EventFederationStore

Improve caching for read_marker API

We add a new storage function to get a paritcular type of room account
data. This allows us to prefill the cache when updating that acount
data.

Move RoomMemberHandler out of Handlers

Split out stream store

Calculate stream_ordering_month_ago correctly on workers

Split up RoomStore

Rewrite make_deferred_yieldable avoiding inlineCallbacks