It doesn't really belong under rest/client/v1 any more.

Rewrite this so that it doesn't hammer the database.

make sure we store the name of the server the keys came from, rather than the
origin server, after doing a fetch-from-perspectives.

This is a bit fiddly due to the keyring doing weird things with logcontexts.

Remove presence list support as per MSC 1819

Hopefully this time we really will fix #4422.

We need to make sure that the cache on
`get_rooms_for_user_with_stream_ordering` is invalidated *before* the
SyncHandler is notified for the new events, and we can now do so reliably via
the `events` stream.

test threepid checking

Collect all the things that make room-versions different to one another into
one place, so that it's easier to define new room versions.

Redo of https://github.com/matrix-org/synapse/pull/4840

Make sure that they are sent correctly over the replication stream.

Fixes: #4898

I don't have a database with the same name as my user, so leaving the database
name unset fails.

While we're at it, clear out some unused stuff in the test setup.

Rather than stubbing out the access_log, make it actually log the requests,
which makes it a lot more obvious what is going on during tests.

Rate-limit outgoing read-receipts as per #4730.