Intern table column names once

Add stream_id index to device_lists_outbound_pokes

As this is used for replication streaming

merge in right archlinux package, thanks to @saram-kon from https://github.com/matrix-org/synapse/pull/1956

Don't fetch current state in common case

Currently we fetch the list of current state events whenever we send
something in a room. This is overkill for the common case of persisting
a simple chain of non-state events, so lets handle that case specially.

Fix synapse_port_db failure (fixes #1902)

Cache get_user_devices_from_cache

the aur package is no longer there, community package in arch does exist

Fix #1677 (dynamic thumbnails aspect)

Strip newlines from SQL queries

Fix a race in transaction queue

It was theoretically possible for a PDU to get queued and not sent for ages. On
closer inspection I think there were bigger problems elsewhere, but we might as
well fix this since it's easy.

Fix /context/ visibiltiy rules